THE  LIBRARY  OF 
USEFUL  STORIES 


THE  STORlY  OF  THE 
LIVING  MACHINE 

|j  B|Y 

itSIr  ■’  H.W.CONN 


eemot 


hj  STORAGE 


UNIVERSITY  OF  ILLINOIS 
LIBRARY 


Class 

57o 


Je  07-10M 


Book 

C7tl 


' j) 


Volume 


Digitized  by  the  Internet  Archive 
in  2016 


https  ://arch  ive.org/detai  Is/storyoflivi  ng  macOOconn 


THE 

LIBRARY  OF  USEFUL  STORIES 


Amceba  Polypodia  in  six  successive  stages  of  division. 
Illustrating  the  reproduction  of  the  protozoa  by  simp’e  fission.  The  dark 
spot,  with  white  margin,  is  the  nucleus. 


THE  STORY  OF  THE 
LIVING  MACHINE 


A REVIEW  OF  THE 

CONCLUSIONS  OF  MODERN  BIOLOGY  IN  REGARD 
TO  THE  MECHANISM  WHICH  CONTROLS  THE 
PHENOMENA  OF  LIVING  ACTIVITY 


BY 

H.  W.  CONN 

PROFESSOR  OF  BIOLOGY  IN  WESLEYAN  UNIVERSITY 
AUTHOR  OF  THE  STORY  OF  GERM  LIFE, 
EVOLUTION  OF  TO-DAY,  THE  LIVING  WORLD,  ETC. 


WITH  FIFTY  ILLUSTRATIONS 


NEW  YORK 

D.  APPLETON  AND  COMPANY 
l9°S 


lo 


C7t^ 


Copyright,  1899, 

By  D.  APPLETON  AND  COMPANY. 


lyfjgoj  .2  4 ■'  ^ ■ MorW.e^  \nri  0^ 


PREFACE. 


That  the  living  body  is  a machine  is  a state- 
ment that  is  frequently  made  without  any  very 
accurate  idea  as  to  what  it  means.  On  the  one 
hand  it  is  made  with  a belief  that  a strict  com- 
parison can  be  made  between  the  body  and  an  or- 
dinary, artificial  machine,  and  that  living  beings 
are  thus  reduced  to  simple  mechanisms  ; on  the 
other  hand  it  is  made  loosely,  without  any  special 
thought  as  to  its  significance,  and  certainly  with 
no  conception  that  it  reduces  life  to  a mechanism. 
The  conclusion  that  the  living  body  is  a machine, 
involving  as  it  does  a mechanical  conception  of 
life,  is  one  of  most  extreme  philosophical  impor- 
tance, and  no  one  interested  in  the  philosophical 
conception  of  nature  can  fail  to  have  an  interest 
in  this  problem  of  the  strict  accuracy  of  the  state- 
ment that  the  body  is  a machine.  Doubtless  the 
complete  story  of  the  living  machine  can  not  yet 
be  told;  but  the  studies  of  the  last  fifty  years  have 
brought  us  so  far  along  the  road  toward  its  com- 
pletion that  a review  of  the  progress  made  and  a 


v 


Vi  THE  STORY  OF  THE  LIVING  MACHINE. 

glance  at  the  yet  unexplored  realms  and  un- 
answered questions  will  be  profitable.  For  this 
purpose  this  work  is  designed,  with  the  hope  that 
it  may  give  a clear  idea  of  the  trend  of  recent 
biological  science  and  of  the  advances  made  to- 
ward the  solution  of  the  problem  of  life. 

Middletown,  Conn.,  U.  S.  A. 

October  /,  1898, 


CONTENTS. 


PAGE 

Introduction  — Biology  a new  science — Historical 
biology  — Conservation  of  energy — Evolution  — 
Cytology — New  aspects  of  biology — The  mechanical 
nature  of  living  organisms — Significance  of  the  new 
biological  problems — Outline  of  the  subject  . . i 

PART  I. 

THE  RUNNING  OF  THE  LIVING  MACHINE. 

CHAPTER  I. 

IS  THE  BODY  A MACHINE? 

What  is  a machine  ? — A general  comparison  of  a body  and 
a machine — Details  of  the  action  of  the  machine — 
Physical  explanation  of  the  chief  vital  functions — 

The  living  body  is  a machine — The  living  machine 
constructive  as  well  as  destructive — The  vital  factor  . 19 

CHAPTER  II. 

THE  CELL  AND  PROTOPLASM. 

Vital  properties — The  discovery  of  cells — The  cell  doc- 
trine— The  cell — The  cellular  structure  of  organisms 
— The  cell  wall — Protoplasm — The  reign  of  proto- 
plasm— The  decline  of  the  reign  of  protoplasm— The 
structure  of  protoplasm — The  nucleus — Centrosome 
— Function  of  the  nucleus — Cell  division  or  karyoki- 
nesis — Fertilization  of  the  egg — The  significance  of 

vii 


yiii  THE  STORY  OF  THE  LIVING  MACHINE. 


page 

fertilization — What  is  protoplasm  ? — Reaction  against 
the  cell  doctrine — Fundamental  vital  activities  as 
located  in  cells — Summary 54 


PART  II. 

THE  BUILDING  OF  THE  LIVING  MACHINE. 
CHAPTER  III. 

THE  FACTORS  CONCERNED  IN  THE  BUILDING  OF  THE  LIVING 
MACHINE. 

History  of  the  living  machine — Evidence  for  this  history 
— Historical — Embryological — Anatomical  — Signifi- 
cance of  these  sources  of  history — Forces  at  work  in 
the  building  of  the  living  machine — Reproduction — 
Heredity — Variation  — Inheritance  of  variations  — 
Method  of  machine  building — Migration  and  isola- 
tion— Direct  influence  of  environment — Consciousness 
— Summary  of  Nature's  power  of  building  machines 
— The  origin  of  the  cell  machine — General  summary  . 131 


LIST  OF  ILLUSTRATIONS. 


FIGURE  PAGE 

Amoeba  Polypodia  in  six  successive  stages  of  divi- 
sion ......  Frontispiece 

1.  Figure  illustrating  osmosis 30 

2.  Figure  illustrating  osmosis  . . . ‘ . 31 

3.  Diagram  of  the  intestinal  walls  . . . . .32 

4.  Diagram  of  a single  villus  ......  33 

5.  Enlarged  figure  of  four  cells  in  the  villus  membrane  . 33 

6.  A bit  of  muscle  showing  blood-vessels  . . .36 

7.  A bit  of  bark  showing  cellular  structure  . . .61 

8.  Successive  stages  in  the  division  of  the  developing 

egg 63 

9.  A typical  cell 65 

10.  Cells  at  a root  tip  .......  66 

11.  Section  of  a leaf  showing  cells  of  different  shapes  . 66 

12.  Plant  cells  with  thick  walls,  from  a fern  . . .67 

13.  Section  of  potato  .......  67 

14.  Various  shaped  wood  cells  from  plant  tissue  . . 68 

15.  A bit  of  cartilage  .......  68 

16.  Frogs’  blood  ........  69 

17.  A bit  of  bone  ........  69 

18.  Connective  tissue  .......  70 

19.  A piece  of  nerve  fibre  ......  70 

20.  A muscle  fibre  ........  71 

21.  A complex  cell,  vorticella  ......  71 

22.  An  amoeba  ........  73 

23.  A cell  as  it  appears  to  the  mo  fern  microscope  . . 86 

24.  A cell  cut  into  pieces,  each  containing  a bit  of 

nucleus 89 

25.  A cell  cut  in  pieces,  only  one  of  which  contains  any 

nucleus 90 

26.  Different  forms  of  nucleii  ......  93 


27  and  28.  Two  stages  in  cell  division 


96 


IX 


X 


THE  STORY  OF  THE  LIVING  MACHINE. 


FIGURE 

29  and  30.  Stages  in  cell  division 

31  and  32.  Latest  stages  in  cell  division  . 

33.  An  egg 

34  and  35.  Stages  in  the  process  of  fertilization  of  the 

egg  • *. 

36  and  37.  Stages  in  the  process  of  fertilization  of  the 

egg  • • 

38,  39,  and  40.  Stages  in  fertilization  of  the  egg 

41  and  42.  Latest  stages  in  the  fertilization  of  the  egg  . 

43  and  44.  Two  stages  in  the  division  of  the  egg  . 

45.  A group  of  cells  resulting  from  division,  the  first  step 

in  machine  building  ...... 

46.  A later  step  in  machine  building,  the  gastrula  . 

47.  The  arm  of  a monkey  ...... 

48.  The  arm  of  a bird  ....... 

49.  The  arm  of  an  ancient  half-bird,  half-reptile  animal  . 

50.  Diagram  to  illustrate  the  principle  of  heredity  . 


PAGE 

98 

100 

103 

104 

105 

106 

109 

hi 

135 

135 

144 

144 

144 

156 


THE  STORY 

OF  THE  LIVING  MACHINE. 


INTRODUCTION. 

Biology  a New  Science. — In  recent  years  biol- 
ogy has  been  spoken  of  as  a new  science.  Thirty 
years  ago  departments  of  biology  were  practically 
unknown  in  educational  institutions.  To-day  none 
of  our  higher  institutions  of  learning  considers 
itself  equipped  without  such  a department.  This 
seems  to  be  somewhat  strange.  Biology  is  sim- 
ply the  study  of  living  things;  and  living  nature 
has  been  studied  as  long  as  mankind  has  studied 
anything.  Even  Aristotle,  four  hundred  years  be- 
fore Christ,  classified  living  things.  From  this 
foundation  down  through  the  centuries  living  phe- 
nomena have  received  constant  attention.  Recent 
centuries  have  paid  more  attention  to  living  things 
than  to  any  other  objects  in  nature.  Linnaeus 
erected  his  systems  of  classification  before  modern 
chemistry  came  into  existence ; the  systematic 
study  of  zoology  antedated  that  of  physics;  and 
long  before  geology  had  been  conceived  in  its 
modern  form,  the  animal  and  vegetable  kingdoms 
had  been  comprehended  in  a scientific  system. 
How,  then,  can  biology  be  called  a new  science 
when  it  is  older  than  all  the  others? 

There  must  be  some  reason  why  this,  the  oldest 
of  all,  has  been  recently  called  a new  science,  and 
some  explanation  of  the  fact  that  it  has  only  re- 

i 


2 THE  STORY  OF  THE  LIVING  MACHINE. 

cently  advanced  to  form  a distinct  department  in 
our  educational  system.  The  reason  is  not  diffi- 
cult to  find.  Biology  is  a new  science,  not  be- 
cause the  objects  it  studies  are  new,  but  because 
it  has  adopted  a new  relation  to  those  objects  and 
is  studying  them  from  a new  standpoint.  Ani- 
mals and  plants  have  been  studied  long  enough, 
but  not  as  we  now  study  them.  Perhaps  the  new 
attitude  adopted  toward  living  nature  may  be 
tersely  expressed  by  saying,  that  in  the  past  it  has 
been  studied  as  at  rest , while  to-day  it  is  studied 
as  in  motion.  The  older  zoologists  and  botanists 
confined  themselves  largely  to  the  study  of  ani- 
mals and  plants  simply  as  so  many  museum  speci- 
mens to  be  arranged  on  shelves  with  appropriate 
names.  The  modern  biologist  is  studying  these 
same  objects  as  intensely  active  beings  and  as 
parts  of  an  ever-changing  history.  To  the  stu- 
dent of  natural  history  fifty  years  ago,  animals  and 
plants  were  objects  to  be  classified ; to  the  biologist 
of  to-day,  they  are  objects  to  be  explained. 

To  understand  this  new  attitude,  a brief  review 
of  the  history  of  the  fundamental  features  of 
philosophical  thought  will  be  necessary.  When, 
long  ago,  man  began  to  think  upon  the  phenom- 
ena of  nature,  he  was  able  to  understand  almost 
nothing.  In  his  inability  to  comprehend  the  ac- 
tivities going  on  around  him  he  came  to  regard 
the  forces  of  nature  as  manifestations  of  some 
supernatural  beings.  This  was  eminently  natural. 
He  had  a direct  consciousness  of  his  own  power 
to  act,  and  it  was  natural  for  him  to  assume  that 
the  activities  going  on  around  him  were  caused 
by  similar  powers  on  the  part  of  some  being  like 
himself,  only  superior  to  him.  Thus  he  came  to 
fill  the  unseen  universe  with  gods  controlling  the 


INTRODUCTION. 


3 


forces  of  nature.  The  wind  was  the  breath  of  one 
god,  and  the  lightning  a bolt  thrown  from  the 
hands  of  another. 

With  advancing  thought  the  ideas  of  polythe- 
ism later  gave  place  to  the  nobler  conception  of 
monotheism.  But  for  a long  time  yet  the  same 
ideas  of  the  supernatural,  as  related  to  the  natu- 
ral, retained  their  place  in  man’s  philosophy. 
Those  phenomena  which  he  thought  he  could 
understand  were  looked  upon  as  natural,  while 
those  which  he  could  not  understand  were  looked 
upon  as  supernatural,  and  as  produced  by  the  di- 
rect personal  activity  of  some  divine  agency.  As 
the  centuries  passed,  and  man’s  power  of  observa- 
tion became  keener  and  his  thinking  more  logical, 
many  of  the  hitherto  mysterious  phenomena  be- 
came intelligible  and  subject  to  simple  explana- 
tions. As  fast  as  this  occurred  these  phenomena 
were  unconscious^  taken  from  the  realm  of  the 
supernatural  and  placed  among  natural  phenom- 
ena which  could  be  explained  by  natural  laws. 
Among  the  first  mysteries  to  be  thus  compre- 
hended by  natural  law  were  those  of  astronomy. 
The  complicated  and  yet  harmonious  motions  of 
the  heavenly  bodies  had  hitherto  be’en  inexplica- 
ble. To  explain  them  many  a sublime  concep- 
tion of  almighty  power  had  arisen,  and  the  study 
of  the  heavenly  bodies  ever  gave  rise  to  the 
highest  thoughts  of  Deity.  But  Newton’s  law  of 
gravitation  reduced  the  whole  to  the  greatest 
simplicity.  Through  the  law  and  force  of  gravi- 
tation these  mysteries  were  brought  within  the 
grasp  of  human  understanding.  They  ceased  to 
be  looked  upon  longer  as  supernatural,  and  be- 
came natural  phenomena  so  soon  as  the  force  of 
gravitation  was  accepted  as  a part  of  nature. 


4 THE  STORY  OF  THE  LIVING  MACHINE. 

In  other  branches  of  natural  phenomena  the 
same  history  followed.  The  forces  and  laws  of 
chemical  affinity  were  formulated  and  studied,  and 
physical  laws  and  forces  were  comprehended.  As 
these  natural  forces  were  grasped  it  became,  little 
by  little,  evident  that  the  various  phenomena  of 
nature  were  simply  the  result  of  nature's  forces 
acting  in  accordance  with  nature’s  laws.  Phe- 
nomena hitherto  mysterious  were  one  after  an- 
other brought  within  the  realm  of  law,  and  as 
this  occurred  a smaller  and  smaller  portion  of 
them  were  left  within  the  realm  of  the  so-called 
supernatural.  By  the  middle  of  this  century  this 
advance  had  reached  a point  where  scientists,  at 
least,  were  ready  to  believe  that  nature’s  forces 
were  all-powerful  to  account  for  nature’s  phe- 
nomena. Science  had  passed  from  the  reign  of 
mysticism  to  the  reign  of  law. 

But  after  chemistry  and  physics,  with  all  the 
forces  that  they  could  muster,  had  exhausted 
their  powers  in  explaining  natural  phenomena, 
there  apparently  remained  one  class  of  facts  which 
was  still  left  in  the  realm  of  the  supernatural  and 
the  unexplained.  The  phenomena  associated  with 
living  things  remained  nearly  as  mysterious  as 
ever.  Life  appeared  to  be  the  most  inexplicable 
phenomena  of  nature,  and  none  of  the  forces  and 
laws  which  had  been  found  sufficient  to  account 
for  other  departments  of  nature  appeared  to  have 
much  influence  in  rendering  intelligible  the  phe- 
nomena of  life.  Living  organisms  appeared  to 
be  actuated  by  an  entirely  unique  force.  Their 
shapes  and  structure  showed  so  many  marvellous 
adaptations  to  their  surroundings  as  to  render  it 
apparently  certain  that  their  adjustment  must 
have  been  the  result  of  some  intelligent  planning, 


INTRODUCTION* 


5 


and  not  the  outcome  of  blind  force.  Who  could 
look  upon  the  adaptation  of  the  eye  to  light  with- 
out seeing  in  it  the  result  of  intelligent  design  ? 
Adaptation  to  conditions  is  seen  in  all  animals  and 
plants.  These  organisms  are  evidently  compli- 
cated machines  with  their  parts  intricately  adapted 
to  each  other  and  to  surrounding  conditions. 
Apart  from  animals  and  plants  the  only  other 
similarly  adjusted  machines  are  those  which  have 
been  made  by  human  intelligence;  and  the  infer- 
ence seemed  to  be  clear  that  a similar  intelligence 
was  needed  to  account  for  the  living  machine.  The 
blind  action  of  physical  forces  seemed  inadequate. 
Thus  the  phenomena  of  life,  which  had  been  stud- 
ied longer  than  any  other  phase  of  nature,  con- 
tinued to  stand  aloof  from  the  rest  and  refused  to 
fall  into  line  with  the  general  drift  of  thought. 
The  living  world  seemed  to  give  no  promise  of 
being  included  among  natural  phenomena,  but 
still  persisted  in  retaining  its  supernatural  as- 
pect. 

It  is  the  attempt  to  explain  the  phenomena  of 
the  living  world  by  the  same  kind  of  natural  forces 
that  have  been  adequate  to  account  for  other 
phenomena,  that  has  created  modern  Biology.  So 
long  as  students  simply  studied  animals  and  plants 
as  objects  for  classification,  as  museum  objects,  or 
as  objects  which  had  been  stationary  in  the  his- 
tory of  nature,  so  long  were  they  simply  follow- 
ing along  the  same  lines  in  which  their  prede- 
cessors had  been  travelling.  But  when  once  they 
began  to  ask  if  living  nature  were  not  perhaps 
subject  to  an  intelligent  explanation,  to  study 
living  things  as  part  of  a general  history  and  to 
look  upon  them  as  active  moving  objects  whose  mo- 
tion and  whose  history  might  perhaps  be  accounted 


6 THE  STORY  OF  THE  LIVING  MACHINE. 

for,  then  at  once  was  created  a new  department  of 
thought  and  a new  science  inaugurated. 

Historical  Geology. — Preparation  had  been  made 
for  this  new  method  of  studying  life  by  the  for- 
mulation of  a number  of  important  scientific  dis- 
coveries. Prominent  among  these  stood  historical 
geology.  That  the  earth  had  left  a record  of  her 
history  in  the  rocks  in  language  plain  enough  to 
be  read  appears  to  have  been  impressed  upon 
scientists  in  the  last  of  the  century.  That  the 
earth  has  had  a history  and  that  man  could  read 
it  became  more  and  more  thoroughly  understood 
as  the  first  decades  of  this  century  passed.  The 
reading  of  that  history  proved  a somewhat  diffi- 
cult task.  It  was  written  in  a strange  language, 
and  it  required  many  years  to  discover  the  key 
to  the  record.  But  under  the  influence  of  the 
writings  of  Lyell,  just  before  the  middle  of  the 
century,  it  began  to  appear  that  the  key  to  this  lan- 
guage is  to  be  found  by  simply  opening  the  eyes 
and  observing  what  is  going  on  around  us  to-day. 
A more  extraordinary  and  more  important  discov- 
ery has  hardly  ever  been  made,  for  it  contained 
the  foundation  of  nearly  all  scientific  discoveries 
which  have  been  made  since.  This  discovery  pro- 
claimed that  an  application  of  the  forces  still  at 
work  to-day  on  the  earth’s  surface,  but  continued 
throughout  long  ages,  will  furnish  the  interpreta- 
tion of  the  history  written  in  the  rocks,  and  thus 
an  explanation  of  the  history  of  the  earth  itself. 
The  slow  elevation  of  the  earth’s  crust,  such  as  is 
still  going  on  to-day,  would,  if  continued,  produce 
mountains  ; and  the  washing  away  of  the  land  by 
rains  and  floods,  such  as  we  see  all  around  us, 
would,  if  continued  through  the  long  centuries, 
produce  the  valleys  and  gorges  which  so  astound 


INTRODUCTION. 


7 


us.  The  explanation  of  the  past  is  to  be  found  in 
the  present.  But  this  geological  history  told  of  a 
history  of  life  as  well  as  a history  of  rocks.  The 
history  of  the  rocks  has  indeed  been  bound  up  in 
the  history  of  life,  and  no  sooner  did  it  appear 
that  the  earth’s  crust  has  had  a readable  history 
than  it  appeared  that  living  nature  had  a parallel 
history.  If  the  present  is  a key  to  the  past  in 
interpreting  geological  history,  should  not  the 
same  be  true  of  this  history  of  life?  It  was  in- 
evitable that  problems  of  life  should  come  to  the 
front,  and  that  the  study  of  life  from  the  dynam- 
ical standpoint,  rather  than  a statical,  should  en- 
sue. Modern  biology  was  the  child  of  historical 
geology. 

But  historical  geology  alone  could  never  have 
led  to  the  dynamical  phase  of  modern  biology. 
Three  other  conceptions  have  contributed  in  an 
even  greater  degree  to  the  development  of  this 
science. 

Conservation  of  Energy. — The  first  of  these  was 
the  doctrine  of  conservation  of  energy  and  the 
correlation  of  forces.  This  doctrine  is  really  quite 
simple,  and  may  be  outlined  as  follows:  In  the 
universe,  as  we  know  it,  there  exists  a certain 
amount  of  energy  or  power  of  doing  work.  This 
amount  of  energy  can  neither  be  increased  nor 
decreased ; energy  can  no  more  be  created  or 
destroyed  than  matter.  It  exists,  however,  in  a 
variety  of  forms,  which  may  be  either  active  or 
passive.  In  the  active  state  it  takes  some  form 
of  motion.  The  various  forces  which  we  recog- 
nize in  nature — heat,  light,  electricity,  chemism, 
etc. — are  simply  forms  of  motion,  and  thus  forms 
of  this  energy.  These  various  types  of  energy, 
being  only  expressions  of  the  universal  energy, 


8 THE  STORY  OF  THE  LIVING  MACHINE. 

are  convertible  into  each  other  in  such  a way 
that  when  one  disappears  another  appears.  A 
cannon  ball  flying  through  the  air  exhibits  energy 
of  motion;  but  it  strikes  an  obstacle  and  stops. 
The  motion  has  apparently  stopped,  but  an  ex- 
amination shows  that  this  is  not  the  case.  The 
cannon  ball  and  the  object  it  strikes  have  been 
heated,  and  thus  the  motion  of  the  ball  has  simply 
been  transformed  into  a different  form  of  motion, 
which  we  call  heat.  Or,  again,  the  heat  set  free 
under  the  locomotive  boiler  is  converted  by  ma- 
chinery into  the  motion  of  the  locomotive.  By 
still  different  mechanism  it  may  be  converted  into 
electric  force.  All  forms  of  motion  are  readily 
convertible  into  each  other,  and  each  form  in 
which  energy  appears  is  only  a phase  of  the  total 
energy  of  nature. 

A second  condition  of  energy  is  energy  at  rest, 
or  potential  energy.  A stone  on  the  roof  of  a 
house  is  at  rest,  but  by  virtue  of  its  position  it 
has  a certain  amount  of  potential  energy,  since,  if 
dislodged,  it  will  fall  to  the  ground,  and  thus  de- 
velop energy  of  motion.  Moreover,  it  required  to 
raise  the  stone  to  the  roof  the  expenditure  of  an 
amount  of  energy  exactly  equal  to  that  which 
will  reappear  if  the  stone  is  allowed  to  fall  to  the 
ground.  So  in  a chemical  molecule,  like  fat,  there 
is  a store  of  potential  energy  which  may  be  made 
active  by  simply  breaking  the  molecule  to  pieces 
and  setting  it  free.  This  occurs  when  the  fat 
burns  and  the  energy  is  liberated  as  heat.  But  it 
required  at  some  time  the  expenditure  of  an  equal 
amount  of  energy  to  make  the  molecule.  When 
the  molecule  of  fat  was  built  in  the  plant  which 
produced  it,  there  was  used  in  its  construction  an 
amount  of  solar  energy  exactly  equivalent  to  the 


INTRODUCTION. 


9 


energy  which  may  be  liberated  by  breaking  the 
molecule  to  pieces.  The  total  sum  of  the  active 
and  potential  energy  in  the  universe  is  thus  at  all 
times  the  same. 

This  magnificent  conception  has  become  the 
cornerstone  of  modern  science.  As  soon  as  con- 
ceived it  brought  at  once  within  its  grasp  all  forms 
of  energy  in  nature.  It  is  primarily  a physical 
doctrine,  and  has  been  developed  chiefly  in  con- 
nection with  the  physical  sciences.  But  it  shows 
at  once  a possible  connection  between  living  and 
non-living  nature.  The  living  organism  also  ex- 
hibits motion  and  heat,  and,  if  the  doctrine  of 
the  conservation  of  energy  be  true,  this  energy 
must  be  correlated  with  other  forms  of  energy. 
Here  is  a suggestion  that  the  same  laws  control 
the  living  and  the  non-living  world  ; and  a sus- 
picion that  if  we  can  find  a natural  explanation 
of  the  burning  of  a piece  of  coal  and  the  motion 
of  a locomotive,  so,  too,  we  may  find  a natural 
explanation  of  the  motion  of  a living  machine. 

Evolution. — A second  conception,  whose  influ- 
ence upon  the  development  of  biology  was  even 
greater,  was  the  doctrine  of  evolution.  It  is  true 
that  the  doctrine  of  evolution  was  no  newT  doc- 
trine with  the  middle  of  this  century,  for  it  had 
been  conceived  somewhat  vaguely  before.  But 
until  historical  geology  had  been  formulated,  and 
until  the  idea  of  the  unity  of  nature  had  dawned 
upon  the  minds  of  scientists,  the  doctrine  of  evo- 
lution had  little  significance.  It  made  little  differ- 
ence in  our  philosophy  whether  the  living  organ- 
isms were  regarded  as  independent  creations  or  as 
descended  from  each  other,  so  long  as  they  were 
looked  upon  as  a distinct  realm  of  nature  without 
connection  with  the  rest  of  nature’s  activity.  If 


IO  THE  STORY  OF  THE  LIVING  MACHINE. 

they  are  distinct  from  the  rest  of  nature,  and  there- 
fore require  a distinct  origin,  it  makes  little  differ- 
ence whether  we  looked  upon  that  origin  as  a sin- 
gle originating  point  or  as  thousands  of  independ- 
ent creations.  But  so  soon  as  it  appeared  that  the 
present  condition  of  the  earth’s  crust  was  formed 
by  the  action  of  forces  still  in  existence,  and  so 
soon  as  it  appeared  that  the  forces  outside  of  liv- 
ing forces,  including  astronomical,  physical  and 
chemical  forces,  are  all  correlated  with  each 
other  as  parts  of  the  same  store  of  energy,  then 
the  problem  of  the  origin  of  living  things  as- 
sumed a new  meaning.  Living  things  became 
then  a part  of  nature,  and  demanded  to  be  in- 
cluded in  the  same  general  category.  The  reign 
of  law,  which-  was  claiming  that  all  nature’s 
phenomena  are  the  result  of  natural  rather  than 
supernatural  powers,  demanded  some  explanation 
of  the  origin  of  living  things.  Consequently, 
when  Darwin  pointed  out  a possible  way  in  which 
living  phenomena  could  thus  be  included  in  the 
realm  of  natural  law,  science  was  ready  and 
anxious  to  receive  his  explanation. 

Cytology. — A third  conception  which  contrib- 
uted to  the  formulation  of  modern  biology  was 
derived  from  the  facts  discovered  in  connection 
with  the  organic  cell  and  protoplasm.  The  sig- 
nificance of  these  facts  we  shall  notice  later,  but 
here  we  may  simply  state  that  these  discoveries 
offered  to  students  simplicity  in  the  place  of  com- 
plexity. The  doctrine  of  cells  and  protoplasm 
appeared  to  offer  to  biologists  no  longer  the  com- 
plicated problems  which  were  associated  with  ani- 
mals and  plants,  but  the  same  problems  stripped 
of  all  side  issues  and  reduced  to  their  lowest  terms. 
This  simplifying  of  the  problems  proved  to  be  an 


INTRODUCTION. 


II 


extraordinary  stimulus  to  the  students  who  were 
trying  to  find  some  way  of  understanding  life. 

New  Aspects  of  Biology. — These  three  concep- 
tions seized  hold  of  the  scientific  world  at  periods 
not  very  distant  from  each  other,  and  their  influ- 
ence upon  the  study  of  living  nature  was  imme- 
diate and  extraordinary.  Living  things  now  came 
to  be  looked  upon  not  simply  as  objects  to  be 
catalogued,  but  as  objects  which  had  a history, 
and  a history  which  was  of  interest  not  merely  in 
itself,  but  as  a part  of  a general  plan.  They  were 
no  longer  studied  as  stationary,  but  as  moving 
phases  of  nature.  Animals  were  no  longer  looked 
upon  simply  as  beings  now  existing,  but  as  the 
results  of  the  action  of  past  forces  and  as  the 
foundation  of  a different  series  of  beings  in  the 
future.  The  present  existing  animals  and  plants 
came  to  be  regarded  simply  as  a step  in  the  long 
history  of  the  universe.  It  appeared  at  once  that 
the  study  of  the  present  forms  of  life  would  offer 
us  a means  of  interpreting  the  past  and  perhaps 
predicting  the  future. 

In  a short  time  the  entire  attitude  which  the 
student  assumed  toward  living  phenomena  had 
changed.  Biological  science  assumed  new  guises 
and  adopted  new  methods.  Even  the  problems 
which  it  tried  to  solve  were  radically  changed. 
Hitherto  the  attempt  had  been  made  to  find  in- 
stances of  purpose  in  nature.  The  marvellous 
adaptations  of  living  beings  to  their  conditions 
had  long  been  felt,  and  the  study  of  the  purposes 
of  these  adaptations  had  inspired  many  a mag- 
nificent conception.  But  now  the  scientist  lost 
sight  of  the  purpose  in  hunting  for  the  cause . 
Natural  law  is  blind  and  can  have  no  purpose. 
To  the  scientist,  filled  with  the  thought  of  the 


12  THE  STORY  OF  THE  LIVING  MACHINE. 

reign  of  law,  purpose  could  not  exist  in  nature. 
Only  cause  and  effect  appeal  to  him.  The  present 
phenomena  are  the  result  of  forces  acting  in  the 
past,  and  the  scientist’s  search  should  be  not  for 
the  purpose  of  an  adaptation,  but  for  the  action 
of  the  forces  which  produced  it.  To  discover  the 
forces  and  laws  which  led  to  the  development  of 
the  present  forms  of  animals  and  plants,  to  ex- 
plain the  method  by  which  these  forces  of  nature 
have  acted  to  bring  about  present  results,  these 
became  the  objects  of  scientific  research.  It  no 
longer  had  any  meaning  to  find  that  a special 
organ  was  adapted  to  its  conditions;  but  it  was 
necessary  to  find  out  how  it  became  adapted. 
The  difference  in  the  attitude  of  these  two  points 
of  view  is  world-wide.  The  former  fixes  the  at- 
tention upon  the  end,  the  latter  upon  the  means 
by  which  the  end  was  attained ; the  former  is 
what  we  sometimes  call  teleological , the  latter  sci- 
entific ; the  former  was  the  attitude  of  the  study 
of  animals  and  plants  before  the  middle  of  this 
century,  the  latter  the  spirit  which  actuates  mod- 
ern biology. 

The  Mechanical  Nature  of  Living  Organisms. — 

This  new  attitude  forced  many  new  problems  to 
the  front.  Foremost  among  them  and  fundamen- 
tal to  them  all  were  the  questions  as  to  the  me- 
chanical nature  of  living  organisms.  The  law  of 
the  correlation  of  force  told  that  the  various 
forms  of  energy  which  appear  around  us — light, 
heat,  electricity,  etc. — are  all  parts  of  one  common 
store  of  energy  and  convertible  into  each  other. 
The  question  whether  vital  energy  is  in  like  man- 
ner correlated  with  other  forms  of  energy  was 
now  extremely  significant.  Living  forces  had  been 
considered  as  standing  apart  from  the  rest  of  na- 


INTRODUCTION. 


13 


ture.  Vital  force , or  vitality , had  been  thought  of 
as  something  distinct  in  itself ; and  that  there  was 
any  measurable  relation  between  the  powers  of 
the  living  organism  and  the  forces  of  heat  and 
chemical  affinity  was  of  course  unthinkable  be- 
fore the  formulation  of  the  doctrine  of  the  corre- 
lation of  forces.  But  as  soon  as  that  doctrine  was 
understood  it  began  to  appear  at  once  that,  to  a 
certain  extent  at  least,  the  living  body  might  be 
compared  to  a machine  whose  function  is  simply 
to  convert  one  kind  of  energy  into  another.  A 
steam  engine  is  fed  with  fuel.  In  that  fuel  is  a 
store  of  energy  deposited  there  perhaps  centuries 
ago.  The  rays  of  the  sun,  shining  on  the  world 
in  earlier  ages,  were  seized  upon  by  the  growing 
plants  and  stored  away  in  a potential  form  in  the 
wood  which  later  became  coal.  This  coal  is  placed 
in  the  furnace  of  the  steam  engine  and  is  broken 
to  pieces  so  that  it  can  no  longer  hold  its  store 
of  energy,  which  is  at  once  liberated  in  its  active 
form  as  heat.  The  engine  then  takes  the  energy 
thus  liberated,  and  as  a result  of  its  peculiar  mech- 
anism converts  it  into  the  motion  of  its  great  fly- 
wheel. With  this  notion  clearly  in  mind  the  ques^ 
tion  forces  itself  to  the  front  whether  the  same 
facts  are  not  true  of  the  living  animal  organism. 
It,  too,  is  fed  with  food  containing  a store  of  en- 
ergy; and  should  we  not  regard  it,  like  the  steam 
engine,  simply  a machine  for  converting  this  po- 
tential energy  into  motion,  heat,  or  some  other 
active  form  ? This  problem  of  the  correlation 
of  vital  and  physical  forces  is  inevitably  forced 
upon  us  with  the  doctrine  of  the  correlation  of 
forces.  Plainly,  however,  such  questions  were 
inconceivable  before  about  the  middle  of  the 
nineteenth  century. 


14  THE  story  of  the  living  machine. 


This  mechanical  conception  of  living  activity 
was  carried  even  farther.  Under  the  lead  of  Hux- 
ley there  arose  in  the  seventh  decade  of  the  cen- 
tury a view  of  life  which  reduced  it  to  a pure 
mechanism.  The  microscope  had,  at  that  time, 
just  disclosed  the  universal  presence  in  living 
things  of  that  wonderful  substance,  protoplasm. 
This  material  appeared  to  be  a homogeneous  sub- 
stance, and  a chemical  study  showed  it  to  be  made 
of  chemical  elements  united  in  such  a way  as  to 
show  close  relation  to  albumens.  It  appeared  to 
be  somewhat  more  complex  than  ordinary  albu- 
men, but  it  was  looked  upon  as  a definite  chemical 
compound,  or,  perhaps,  as  a simple  mixture  of 
compounds.  Chemists  had  shown  that  the  proper- 
ties of  compounds  vary  with  their  composition, 
and  that  the  more  complex  the  compound  the 
more  varied  its  properties.  It  was  a natural  con- 
ception, therefore,  that  protoplasm  was  a complex 
chemical  compound,  and  that  its  vital  properties 
were  simply  the  chemical  properties  resulting 
from  its  composition.  Just  as  water  possesses  the 
power  of  becoming  solid  at  certain  temperatures, 
so  protoplasm  possesses  the  power  of  assimilating 
food  and  growing;  and,  since  we  do  not  doubt 
that  the  properties  of  water  are  the  result  of  its 
chemical  composition,  so  we  may  also  assume  that 
the  vital  properties  of  protoplasm  are  the  result 
of  its  chemical  composition.  It  followed  from 
this  conclusion  that  if  chemists  ever  succeeded  in 
manufacturing  the  chemical  compound,  proto- 
plasm, it  would  be  alive.  Vital  phenomena  were 
thus  reduced  to  chemical  and  mechanical  problems. 

These  ideas  arose  shortly  after  the  middle  of 
the  century,  and  have  dominated  the  development 
of  biological  science  up  to  the  present  time.  It 


INTRODUCTION. 


15 


is  evident  that  the  aim  of  biological  study  must 
be  to  test  these  conceptions  and  carry  them  out 
into  details.  The  chemical  and  mechanical  laws 
of  nature  must  be  applied  to  vital  phenomena  in 
order  to  see  whether  they  can  furnish  a satisfac- 
tory explanation  of  life.  Are  the  laws  and  forces 
of  chemistry  sufficient  to  explain  digestion  ? Are 
the  laws  of  electricity  applicable  to  an  under- 
standing of  nervous  phenomena  ? Are  physical 
and  chemical  forces  together  sufficient  to  explain 
life  ? Can  the  animal  body  be  properly  regarded 
as  a machine  controlled  by  mechanical  laws  ? Or, 
on  the  other  hand,  are  there  some  phases  of  life 
which  the  forces  of  chemistry  and  physics  cannot 
account  for?  Are  there  limits  to  the  application 
of  natural  law  to  explain  life?  Can  there  be 
found  something  connected  with  living  beings 
which  is  force  but  not  correlated  with  the  ordinary 
forms  of  energy  ? Is  there  such  a thing  as  vital 
energy , or  is  the  so-called  vital  force  simply  a 
name  which  we  have  given  to  the  peculiar  mani- 
festations of  ordinary  energy  as  shown  in  the 
substance  protoplasm?  These  are  some  of  the 
questions  that  modern  biology  is  trying  to  an- 
swer, and  it  is  the  existence  of  such  questions 
which  has  made  modern  biology  a new  science. 
Such  questions  not  only  did  not,  but  could  not, 
have  arisen  before  the  doctrines  of  the  conserva- 
tion of  energy  and  evolution  had  made  their  im- 
pression upon  the  thought  of  the  world. 

Significance  of  the  New  Biological  Problems. — It 
is  further  evident  that  the  answers  to  these  ques- 
tions will  have  a significance  reaching  beyond 
the  domain  of  biology  proper  and  affecting  the 
fundamental  philosophy  of  nature.  The  answer 
will  determine  whether  or  not  we  can  accept  in 


1 6 THE  STORY  OF  THE  LIVING  MACHINE. 

entirety  the  doctrines  of  the  conservation  of  en- 
ergy and  evolution.  Plainly  if  it  should  be  found 
that  the  energy  of  animate  nature  was  not  cor- 
related with  other  forms  of  energy,  this  would 
demand  either  a rejection  or  a complete  modifi- 
cation of  our  doctrine  of  the  conservation  of  en- 
ergy. If  an  animal  can  create  any  energy  within 
itself,  or  can  destroy  any  energy,  we  can  no  longer 
regard  the  amount  of  energy  of  the  universe  as 
constant.  Even  if  that  subtile  form  of  force  which 
we  call  nervous  energy  should  prove  to  be  uncor- 
related with  other  forms  of  energy,  the  idea  of 
the  conservation  of  energy  must  be  changed.  It 
is  even  possible  that  we  must  insist  that  the  still 
more  subtile  form  of  force,  mental  force,  must  be 
brought  within  the  scope  of  this  great  law  in 
order  that  it  be  implicitly  accepted.  This  law  has 
proved  itself  strictly  applicable  to  the  inanimate 
world,  and  has  then  thrust  upon  us  the  various 
questions  in  regard  to  vital  force,  and  we  must 
recognize  that  the  real  significance  of  this  great 
law  must  rest  upon  the  possibility  of  its  applica- 
tion to  vital  phenomena. 

No  less  intimate  is  the  relation  of  these  prob- 
lems to  the  doctrine  of  evolution.  Evolution  tries' 
to  account  for  each  moment  in  the  history  of  the 
world  as  the  result  of  the  conditions  of  the  mo- 
ment before.  Such  a theory  loses  its  meaning 
unless  it  can  be  shown  that  natural  forces  are  suf- 
ficient to  account  for  living  phenomena.  If  the 
supernatural  must  be  brought  in  here  and  there 
to  account  for  living  phenomena,  then  evolution 
ceases  to  have  much  meaning.  It  is  undoubtedly 
a fact  that  the  rapidly  developing  ideas  along  the 
above  mentioned  lines  of  dynamical  biology  have 
been  potent  factors  in  bringing  about,  the  adop- 


INTRODUCTION. 


!7 


tion  of  evolution.  Certain  it  is  that,  had  it  been 
found  that  no  correlation  could  be  traced  between 
vital  and  non-vital  forces,  the  doctrine  of  evolu- 
tion could  not  have  stood,  and  even  now  the 
special  significance  which  we  shall  in  the  end  give 
to  evolution  will  depend  upon  how  we  succeed  in 
answering  the  questions  above  outlined.  The  fact 
is  that  this  problem  of  the  mechanical  explanation 
of  vital . phenomena  forms  the  capstone  of  the 
arch,  the  sides  of  which  are  built  of  the  doc- 
trines of  the  conservation  of  energy  and  the 
theory  of  evolution.  To  the  presentation  of  these 
problems  the  following  pages  will  be  devoted. 
The  fact  that  both  the  doctrine  of  the  conserva- 
tion of  energy  and  that  of  evolution  are  practi- 
cally everywhere  accepted  indicates  that  the  me- 
chanical nature  of  vital  forces  is  regarded  as 
proved.  But  there  are  still  many  questions  which 
are  not  so  easily  answered.  It  will  be  our  pur- 
pose in  the  following  discussion  to  ascertain  just 
what  are  these  problems  in  dynamical  biology  and 
how  far  they  have  been  answered.  Our  object  will 
be  then  in  brief  to  discover  to  what  extent  the 
conception  of  the  living  organism  as  a machine  is 
borne  out  by  the  facts  which  have  been  collected 
in  the  last  quarter  century,  and  to  learn  where,  if 
anywhere,  limits  have  been  found  to  our  possibility 
of  applying  the  forces  of  chemistry  and  physics 
to  an  explanation  of  life.  In  other  words,  we  shall 
try  to  see  how  far  we  have  been  able  to  under- 
stand living  phenomena  in  terms  of  natural  force. 

Outline  of  the  Subject. — The  subject,  as  thus 
presented,  resolves  itself  at  once  into  two  parts. 
That  the  living  organism  is  a machine  is  every- 
where recognized,  although  some  may  still  doubt 
as  to  the  completeness  of  the  comparison.  In  the 


1 8 THE  STORY  OF  THE  LIVING  MACHINE. 

attempt  to  explain  the  phenomena  of  life  we  have 
two  entirely  different  problems.  The  first  is  mani- 
festly to  account  for  the  existence  of  this  machine, 
for  such  a completed  piece  of  mechanism  as  a man 
or  a tree  cannot  be  explained  as  a result  of  simple 
accident,  as  the  existence  of  a rough  piece  of  rock 
might  be  explained.  Its  intricacy  of  parts  and 
their  purposeful  interrelation  demands  explana- 
tion, and  therefore  the  fundamental  problem  is 
to  explain  how  this  machine  came  into  existence. 
The  second  problem  is  simpler,  for  it  is  simply  to 
explain  the  running  of  the  machine  after  it  is 
made.  If  the  organism  is  really  a madhine,  we 
ought  to  be  able  to  find  some  way  of  explaining 
its  actions  as  we  can  those  of  a steam  engine. 

Of  these  two  problems  the  first  is  the  more 
fundamental,  for  if  we  fail  to  find  an  explanation 
for  the  existence  of  the  machine,  our  explanation 
of  its  method  of  action  is  only  partly  satisfactory. 
But  the  second  question  is  the  simpler,  and  must 
be  answered  first.  We  cannot  hope  to  explain  the 
more  puzzling  matter  of  the  origin  of  the  machine 
unless  we  can  first  understand  how  it  acts.  In 
our  treatment  of  the  subject,  therefore,  we  shall 
divide  it  into  two  parts : 

I.  The  Running  of  the  Living  Machine . 

II.  The  Origin  of  the  Living  Machine. 


PART  I. 


THE  RUNNING  OF  THE  LIVING  MACHINE , 


CHAPTER  I. 

IS  THE  BODY  A MACHINE? 

The  problem  before  us  in  this  section  is  to  find 
out  to  what  extent  animals  and  plants  are  ma- 
chines. We  wish  to  determine  whether  the  laws 
and  forces  which  regulate  their  activities  are  the 
same  as  the  laws  and  forces  with  which  we  ex- 
periment in  the  chemical  and  physical  laboratory, 
and  whether  the  principles  of  mechanics  and  the 
doctrine  of  the  conservation  of  energy  apply  equal- 
ly well  in  the  living  machine  and  the  steam  engine. 

It  might  be  inferred  that  the  proper  method  of 
study  would  be  to  confine  our  attention  largely  to 
the  simplest  forms  of  life,  since  the  problems 
would  be  here  less  complicated,  and  therefore  of 
easier  solution.  This,  however,  has  not  been  nor 
can  it  be  the  method  of  study.  Our  knowledge 
of  the  processes  of  life  have  been  derived  largely 
from  the  most  rather  than  the  least  complex 
forms.  We  have  a better  knowledge  of  the  physi- 
ology of  man  and  his  allies  than  any  other  ani- 
mals. The  reason  for  this  is  plain  enough.  In 
the  first  place,  there  is  a value  in  the  knowledge  of 
the  life  activities  of  man  entirely  apart  from  any 
theoretical  aspects,  and  hence  human  physiology 

19 


20  THE  STORY  OF  THE  LIVING  MACHINE. 

has  demanded  attention  for  its  own  sake.  The 
practical  utility  of  human  physiology  has  stimu- 
lated its  study  for  centuries;  and  in  the  last  fifty 
years  of  scientific  progress  it  has  been  human 
physiology  and  that  of  allied  animals  that  has  at- 
tracted the  chief  attention  of  physiologists.  The 
result  is  that  while  the  physiology  of  man  is  toler- 
ably well  known,  that  of  other  animals  is  less  un- 
derstood the  farther  we  get  away  from  man  and 
his  allies.  For  this  reason  most  of  our  knowledge 
of  the  living  body  as  a machine  must  be  derived 
from  the  study  of  man.  This  is,  however,  fortu- 
nate rather  than  otherwise.  In  the  first  place,  it 
enables  us  to  proceed  from  the  known  to  the  un- 
known ; and  in  the  second  place,  more  interest  at- 
taches to  the  problem  as  connected  with  human 
physiology  than  along  any  other  line.  In  our  dis- 
cussion, therefore,  we  shall  refer  chiefly  to  the 
physiology  of  man.  If  we  find  that  the  functions 
of  human  life  are  amenable  to  a mechanical  ex- 
planation we  cannot  hesitate  to  believe  that  this 
will  be  equally  true  of  the  lower  orders  of  nature. 
For  similar  reasons  little  reference  will  be  made 
to  the  mechanism  of  plant  life.  The  structure  of 
the  plant  is  simpler  and  its  activities  are  much 
more  easilly  referable  to  mechanical  principles 
than  are  those  of  animals.  For  these  reasons  it 
will  only  be  necessary  for  us  to  turn  our  attention 
to  the  life  activities  of  the  higher  animals. 

What  is  a Machine  ? — Turning  now  to  our  more 
immediate  subject  of  the  accuracy  of  the  state- 
ment that  the  body  is  a machine,  we  must  first  ask 
what  is  meant  by  a machine  ? A brief  definition 
of  a machine  might  be  as  follows:  A machine  is  a. 
piece  of  apparatus  so  designed  that  it  can  change  one 
kind  of  energy  into  another  for  a definite  purpose. 


IS  THE  BODY  A MACHINE? 


21 


Energy,  as  already  noticed,  is  the  power  of  doing 
work,  and  its  ordinary  active  forms  are  heat,  mo- 
tion, electricity,  light,  etc. ; but  it  may  be  in  a 
passive  or  potential  form,  and  in  this  form  stored 
within  a chemical  molecule.  These  various  forms 
of  energy  are  readily  convertible  into  each  other; 
and  any  form  of  apparatus  designed  for  the  pur- 
pose of  producing  such  a conversion  is  called  a 
machine.  A dynamo  is  thus  a machine  so  adjusted 
that  whem  mechanical  motion  is  supplied  to  it 
the  energy  of  motion  is  converted  into  electricity  ; 
while  an  electromotor,  on  the  other  hand,  is  a 
piece  of  apparatus  so  designed  that  when  electric- 
ity is  applied  to  it,  it  is  converted  into  motion. 
A steam  engine,  again,  is  designed  to  convert 
potential  or  passive  energy  into  active  energy. 
Potential  energy  in  the  form  of  chemical  compo- 
sition (coal)  is  supplied  to  the  engine,  and  this 
energy  is  first  liberated  in  the  active  form  of  heat 
and  then  is  converted  into  the  motion  of  the  great 
fly-wheel.  In  all  these  cases  there  is  no  energy  or 
power  created,  for  the  machine  must  be  always 
supplied  with  an  amount  of  energy  equal  to  that 
which  it  gives  back  in  another  form.  Indeed,  a 
larger  amount  of  energy  must  be  furnished  the 
machine  than  is  expected  back,  for  there  is  always 
an  actual  loss  of  available  energy.  In  the  process 
of  the  conversion  of  one  form  of  energy  into  an- 
other some  of  the  energy,  from  friction  or  other 
cause,  takes  the  form  of  heat,  and  is  then  radiated 
into  space  beyond  our  reach.  It  is,  of  course,  not 
destroyed,  for  energy  cannot  be  destroyed  ; but  it 
has  assumed  a form  called  radiant  heat,  which 
is  not  available  for  our  uses.  A machine  thus 
neither  creates  nor  destroys  energy.  It  receives 
it  in  one  form  and  gives  it  back  in  another  form. 


22  THE  STORY  OF  THE  LIVING  MACHINE. 

with  an  inevitable  loss  of  a portion  of  the  energy 
as  radiant  heat.  With  this  understanding,  we  may 
now  ask  if  the  living  body  can  be  properly  com- 
pared with  a machine. 

A General  Comparison  of  a Body  and  a Machine. 

— That  the  living  body  exhibits  the  ordinary  types 
of  energy  is  of  course  clear  enough  when  we 
remember  that  it  is  always  in  motion  and  is 
always  radiating  heat — two  of  the  most  common 
types  of  physical  energy.  That  this  energy  is 
supplied  to  the  body  as  it  is  to  other  machines,  in 
the  form  of  the  energy  of  chemical  composition, 
will  also  need  no  further  proof  when  it  is  remem- 
bered that  it  is  necessary  to  supply  the  body  with 
appropriate  food  in  order  that  it  may  do  work. 
The  food  we  eat,  like  coal,  represents  so  much 
solar  energy  which  is  stored  up  by  the  agency  of 
plant  life,  and  the  close  comparison  between  feed- 
ing the  body  to  enable  it  to  work  and  feeding  the 
engine  to  enable  it  to  develop  energy  is  so  evident 
that  it  demands  no  further  demonstration.  The 
details  of  the  problem  may,  however,  present  some 
difficulties. 

The  first  question  which  presents  itself  is 
whether  the  only  power  the  body  possesses  is,  as 
in  the  case  with  other  machines,  to  transform 
energy  without  being  able  to  create  or  destroy  it  ? 
Can  every  bit  of  energy  shown  by  the  living  or- 
ganism be  accounted  for  by  energy  furnished  in 
the  food,  and  conversely  can  all  the  energy  fur- 
nished in  the  food  be  found  manifested  in  the 
living  organism  ? 

The  theoretical  answer  to  this  question  in 
terms  of  the  law  of  the  conservation  of  energy  is 
clear  enough,  but  it  is  by  no  means  so  easy  to 
answer  it  by  experimental  data.  To  obtain  ex- 


IS  THE  BODY  A MACHINE? 


2 3 


perimental  demonstration  it  would  be  necessary 
to  make  an  accurate  determination  of  the  amount 
of  energy  an  individual  receives  during  a given 
period,  and  at  the  same  time  a similar  measure- 
ment of  the  amount  of  energy  liberated  in  his 
body  either  as  motion  or  heat.  If  the  body  is  a 
machine,  these  two  should  exactly  balance,  and  if 
they  do  not  balance  it  would  indicate  that  the 
living  organism  either  creates  or  destroys  energy, 
and  is  therefore  not  a machine.  Such  experiments 
are  exceedingly  difficult.  They  must  be  per- 
formed usually  upon  man  rather  than  other  ani- 
mals, and  it  is  necessary  to  inclose  an  individual 
in  an  absolutely  sealed  space  with  arrangements 
for  furnishing  him  with  air  and  food  in  measured 
quantity,  and  with  appliances  for  measuring  accu- 
rately the  work  he  does  and  the  heat  given  off 
from  his  body.  In  addition,  it  is  necessary  to 
measure  the  exact  amount  of  material  he  elimi- 
nates in  the  form  of  carbonic  acid  and  other 
excretions.  Such  experiments  present  many  diffi- 
culties which  have  not  yet  been  thoroughly  over- 
come, but  they  have  been  attempted  by  several 
investigators.  For  the  purpose  of  such  an  ex- 
periment scientists  have  allowed  themselves  to  be 
shut  up  in  a small  chamber  six  or  eight  feet  in 
length,  in  which  their  only  communication  with 
the  outer  world  is  by  telephone  and  through  a 
small  opening  in  the  side  of  the  chamber,  occa- 
sionally opened  for  a second  or  two  to  supply  the 
prisoner  with  food.  In  such  a chamber  they  have 
remained  as  long  as  twelve  days.  In  these  experi- 
ments it  is  necessary  to  take  account  not  only  of 
the  food  eaten,  but  of  the  actual  amount  of  this 
food  which  is  used  by  the  body.  If  the  person 
gains  in  weight,  this  must  mean  that  he  is  storing 
3 


7 


24  THE  story  of  the  living  machine. 

up  in  his  body  material  for  future  use ; while  if  he 
loses  in  weight,  this  means  that  he  is  consuming 
his  own  tissues  for  fuel.  Careful  daily  records  of 
his  weight  must  therefore  be  taken.  Estimates  of 
the  solids,  liquids,  and  gases  given  off  from  his 
body  must  be  obtained,  for  to  carry  out  the  ex- 
periment an  exact  balance  must  be  made  between 
the  income  and  the  outgo.  The  apparatus  devised 
for  such  experiments  has  been  made  very  delicate  ; 
so  delicate,  indeed,  that  the  rising  of  the  individual 
in  the  box  from  his  chair  is  immediately  seen  in 
a rise  in  temperature  of  the  apparatus.  But  even 
with  this  delicacy  the  apparatus  is  comparatively 
coarse,  and  can  measure  only  the  most  apparent 
forms  of  energy.  The  more  subtile  types  of  energy, 
such  as  nervous  force,  if  this  is  to  be  regarded  as 
energy,  do  not  make  any  impression  on  the  appa- 
ratus. 

The  obstacles  in  the  way  of  these  experiments 
do  not  particularly  concern  us,  but  the  general  re- 
sults are  of  the  greatest  significance  for  our  pur- 
pose. While,  for  manifest  reasons,  it  has  not  been 
possible  to  carry  on  these  experiments  for  any 
great  length  of  time,  and  while  the  results  have 
not  yet  been  very  accurately  refined,  they  are  all 
of  one  kind  and  teach  unhesitatingly  one  conclu- 
sion. So  far  as  concerns  measurable  energy  or 
measurable  material,  the  body  behaves  just  like 
any  other  machine.  If  the  body  is  to  do  work  in 
this  respiration  apparatus,  it  does  so  only  by  break- 
ing to  pieces  a certain  amount  of  food  and  using 
the  energy  thus  liberated,  and  the  amount  of  food 
needed  is  proportional  to  the  amount  of  work  done. 
When  the  individual  simply  walks  across  the  floor, 
or  even  rises  from  his  chair,  this  is  accompanied 
by  an  increase  in  the  amount  of  food  material 


IS  THE  BODY  A MACHINE? 


25 


broken  up  and  a consequent  increase  in  the  amount 
of  refuse  matter  eliminated  and  the  heat  given 
off.  The  income  and  outgo  of  the  body  in  both 
matter  and  energy  is  balanced.  If,  during  the 
experimental  period,  it  is  found  that  less  energy 
is  liberated  than  that  contained  in  the  food  assimi- 
lated, it  is  also  found  that  the  body  has  gained  in 
weight,  which  simply  means  that  the  extra  energy 
has  been  stored  in  the  body  for  future  use.  No 
more  energy  can  be  obtained  from  the  body  than 
is  furnished,  and  for  all  furnished  in  the  food  an 
equivalent  amount  is  regained.  There  is  no  trace 
of  any  creation  or  destruction  of  energy.  While, 
on  account  of  the  complexity  of  the  experiment- 
ing, an  absolutely  strict  balance  sheet  cannot  be 
made,  all  the  results  are  of  the  same  nature.  So 
far  as  concerns  measurable  energy,  all  the  facts 
collected  bear  out  the  theoretical  conception  that 
the  living  body  is  to  be  regarded  as  a machine 
which  converts  the  potential  energy  of  chemical 
Composition,  stored  passively  in  its  food,  into  ac- 
tive energy  of  motion  and  heat. 

It  is  found,  however,  that  the  body  is  a machine 
of  a somewhat  superior  grade,  since  it  is  able  to 
convert  this  potential  energy  into  motion  with  less 
loss  than  the  ordinary  machine.  As  noticed  above, 
in  all  machines  a portion  of  the  energy  is  converted 
into  heat  and  rendered  unavailable  by  radiating 
into  space.  In  an  ordinary  engine  only  about  one- 
fifteenth  of  the  energy  furnished  in  the  coal  can 
be  regained  in  the  form  of  motive  power,  the 
rest  being  radiated  from  the  machine  as  heat. 
Some  of  our  better  engines  to-day  utilize  a some- 
what larger  part,  but  most  of  them  utilize  less 
than  one-tenth.  The  experiments  with  the  living 
body  in  the  respiration  apparatus  above  described, 


26  THE  STORY  OF  THE  LIVING  MACHINE. 

give  a means  of  determining  the  proportion  of 
the  energy  furnished  in  the  form  of  food  which 
can.be  utilized  in  the  form  of  motive  force.  This 
figure  appears  to  be  decidedly  larger  than  that 
obtained  by  any  machine  yet  devised  by  man. 

The  conclusion  of  the  matter  up  to  this  point 
is  then  clear.  If  we  leave  out  of  account  the 
phenomena  of  the  nervous  system,  which  we  shall 
consider  presently,  the  general  income  and  outgo  of 
the  body  as  concerns  matter  and  energy  is  such  that  the 
body  must  be  regarded  as  a machine , which , like  other 
machines , simply  transforms  energy  without  creating 
or  destroying  it.  To  this  extent , at  least , animals  con- 
form to  the  laiu  of  the  conservation  of  energy  and  are 
veritable  machines. 

Details  of  the  Action  of  the  Machine. — We  turn 
next  to  some  of  the  subordinate  problems  concern- 
ing the  details  of  the  action  of  the  living  machine. 
We  have  a clear  understanding  of  the  method  of 
action  of  a steam  engine.  Its  mechanism  is  simple, 
and,  moreover,  it  was  designed  by  human  intelli- 
gence. We  can  understand  how  the  force  of 
chemical  affinity  breaks  up  the  chemical  com- 
position of  the  coal,  how  the  heat  thus  liberated  is 
applied  to  the  water  to  vapourize  it ; how  the  va- 
pour is  collected  in  the  boiler  under  pressure  ; how 
this  pressure  is  applied  to  the  piston  in  the  cylin- 
der, and  how  this  finally  results  in  the  revolution 
of  the  fly-wheel.  It  is  true  that  we  do  not  under- 
stand the  underlying  forces  of  chemism,  etc.,  but 
these  forces  certainly  exist  and  are  the  foundation 
of  science.  But  the  mechanism  of  the  engine  is 
intelligible.  Our  understanding  of  it  is  such  that, 
with  the  forces  of  chemistry  and  physics  as  a foun- 
dation, we  can  readily  explain  the  running  of  the 
machine.  Our  next  problem,  therefore,  is  to  see 


IS  THE  BODY  A MACHINE  ? 


27 


if  we  can  in  the  same  way  reach  an  understanding 
of  the  phenomena  of  the  living  machine.  Can  we, 
by  the  use  of  these  same  chemical  and  physical 
forces,  explain  the  activities  taking  place  in  the 
living  organism  ? Can  the  motion  of  the  body, 
for  example,  be  made  as  intelligible  as  the  motion 
of  the  steam  engine  ? 

Physical  Explanation  of  the  Chief  Vital  Func- 
tions.— The  living  machine  is,  of  course,  vastly 
more  complicated  than  the  steam  engine,  and 
there  are  many  different  processes  which  must  be 
considered  separately.  There  is  not  space  in  a 
work  of  this  size  to  consider  them  all  carefully, 
but  we  may  select  a few  of  the  vital  functions  as 
illustrations  of  the  method  which  is  pursued.  It 
will  be  assumed  that  the  fundamental  processes 
of  human  physiology  are  understood  by  the  reader, 
and  we  shall  try  to  interpret  some  of  them  in 
terms  of  chemical  and  physical  force. 

Digestion. — The  first  step  in  this  transformation 
of  fuel  is  the  process  of  digestion.  Now  this  pro- 
cess of  digestion  is  nothing  mysterious,  nor  does  it 
involve  any  peculiar  or  special  forces.  Digestion 
of  food  is  simply  a chemical  change  therein.  The 
food  which  is  taken  into  the  body  in  the  form  of 
sugar,  starch,  fat  or  proteid,  is  acted  upon  by  the 
digestive  juices  in  such  a way  that  its  chemical 
nature  is  slightly  changed.  But  the  changes  that 
thus  occur  are  not  peculiar  to  the  living  body,  since 
they  will  take,  place  equally  well  in  the  chemist’s 
laboratory.  They  are  simply  changes  in  the  mo- 
lecular structure  of  the  food  material,  and  only 
such  changes  as  are  simple  and  familiar  to  the 
chemist.  The  forces  which  effect  the  change  are: 
undoubtedly  those  of  chemical  affinity.  The  only 
feature  of  the  .process  which  is  not  perfectly  intel, 


28  THE  STORY  OF  THE  LIVING  MACHINE. 

eligible  in  terms  of  chemical  law  is  the  nature  of 
the  digestive  juices.  The  digestive  fluids  of  the 
mouth  and  stomach  contain  certain  substances 
which  possess  a somewhat  remarkable  power,  in- 
asmuch as  they  are  able  to  bring  about  the  chem- 
ical changes  which  occur  in  the  digestion  of  food. 
An  example  will  make  this  clearer.  One  of  the 
digestive  processes  is  the  conversion  of  starch  into 
sugar.  The  relation  of  these  two  bodies  is  a very 
simple  one,  starch  being  readily  converted  into 
sugar  by  the  addition  to  its  molecule  of  a molecule 
of  water.  The  change  can  not  be  produced  by 
simply  adding  starch  to  water,  but  the  water  must 
be  introduced  into  the  starch  molecule.  This 
change  can  be  brought  about  in  a variety  of  ways, 
and  is  undoubtedly  effected  by  the  forces  of  chem- 
ical affinity.  Chemists  have  found  simple  methods 
of  producing  this  chemical  union,  and  the  manu- 
facture of  sugar  out  of  starchy  material  has  even 
become  something  of  a commercial  industry.  One 
of  the  methods  by  which  this  change  can  be  pro- 
duced is  by  adding  to  the  starch,  along  with  some 
water,  a little  saliva.  The  saliva  has  the  power  of 
causing  the  chemical  change  to  occur  at  once,  and 
the  molecule  of  water  enters  into  the  starch  mole- 
cule and  forms  sugar.  Now  we  do  not  understand 
how  this  saliva  possesses  this  power  to  induce  the 
chemical  change.  But  apparently  the  process  is 
of  the  simplest  character  and  involves  no  greater 
mystery  than  chemical  affinity.  We  know  that  the 
saliva  contains  a certain  material  called  a ferment, 
which  is  the  active  agent  in  bringing  about  the 
change.  This  ferment  is  not  alive,  nor  does  it 
need  any  living  environment  for  its  action.  It 
can  be  separated  from  the  saliva  in  the  form  of  a 
dry  amorphous  powder,  and  in  this  form  can  be 


IS  THE  BODY  A MACHINE? 


29 


preserved  almost  indefinitely,  retaining  its  power 
to  effect  the  change  whenever  put  under  proper 
conditions.  The  change  of  starch  into  sugar  is 
thus  a simple  chemical  change  occurring  under 
the  influence  of  chemical  affinity  under  certain 
conditions.  One  of  the  conditions  is  the  presence 
of  this  saliva  ferment.  If  we  can  not  exactly  un- 
derstand how  the  ferment  produces  this  action, 
neither  do  we  exactly  understand  how  a spark 
causes  a bit  of  gunpowder  to  explode.  But  we 
can  not  doubt  that  the  latter  is  a purely  natural 
result  of  the  relation  of  chemical  and  physical 
forces,  and  there  is  no  more  reason  for  doubting 
it  in  the  former  case. 

What  is  true  of  the  digestion  of  starch  by  sa- 
liva is  equally  true  of  the  digestion  of  other  foods 
in  the  stomach  and  intestine.  Each  of  the  diges- 
tive juices  contains  a ferment  which  brings  about 
a chemical  change  in  the  food.  The  changes  are 
always  chemical  changes  and  are  the  result  of 
chemical  forces.  Apart  from  the  presence  of  these 
ferments  there  is  really  little  difference  between 
laboratory  chemistry  and  living  chemistry. 

Absorption  of  food. — The  next  function  of  this 
machine  to  attract  our  attention  is  the  absorption 
of  food  from  the  intestine  into  the  blood.  The 
digested  food  is  carried  down  the  alimentary  ca- 
nal in  a purely  mechanical  fashion  by  muscular 
action,  and  when  it  reaches  the  intestine  it  begins 
to  pass  through  its  walls  into  the  blood.  In  this 
absorption  we  find  engaged  another  set  of  forces, 
the  chief  of  which  appears  to  be  the  physical 
force  of  osmosis.  The  force  of  osmosis  has  no 
special  connection  with  life.  If  a membrane  sepa- 
rates two  liquids  of  different  composition  (Fig.  1), 
a force  is  exerted  on  the  liquids,  which  cause  them 


30  THE  STORY  OF  THE  LIVING  MACHINE. 

to  pass  through  the  membrane,  each  passing 
through  the  membrane  into  the  other  compart- 
ment. The  force  which  drives  these  liquids  through 

the  membrane  is 
considerable,  and 
may  sometimes  be 
exerted  against 
considerable  pres- 
sure. A simple  ex- 
periment will  illus- 
trate this  force.  In 
Fig.  2 is  represent- 
ed a membranous 
bag  tightly  fast- 
ened to  a glass 
tube.  The  bag  is 
filled  with  a strong 
solution  of  sugar, 
and  is  immersed  in  a vessel  containing  pure  water. 
Under  these  conditions  some  of  the  sugar  solution 
passes  through  the  bag  into  the  water,  and  some 
of  the  water  passes  from  the  vessel  into  the  bag. 
But  if  the  solution  of  sugar  is  inside  the  bag  and 
the  pure  wTater  outside,  the  amount  of  liquid  pass- 
ing into  the  bag  is  greater  than  the  amount  passing 
out;  the  bag  soon  becomes  distended  and  the  water 
even  rises  in  the  tube  to  a considerable  height  at 
a (Fig.  2).  The  force  here  concerned  is  a force 
known  as  osmosis  or  dialysis , and  is  always  exerted 
when  two  different  solutions  of  certain  substances 
are  separated  from  each  other  by  a membrane. 
The  substances  in  solution  will,  under  these  con- 
ditions, pass  from  the  dense  to  the  weaker  solu- 
tion. The  process  is  a purely  physical  one. 

This  process  of  osmosis  lies  at  the  basis  of 
the  absorption  of  food  from  the  alimentary  canal. 


Fig.  1. — To  illustrate  osmosis.  In  the 
vessel  A is  a solution  of  sugar  ; in  B , 
is  pure  water.  The  two  are  sepa- 
rated by  the  membrane  C.  The 
sugar  passes  through  the  membrane 
into  B . 


IS  THE  BODY  A MACHINE? 


31 


In  the  first  place,  most  of  the  food  when  swal- 
lowed is  not  soluble,  and  therefore  not  capable  of 
osmosis.  But  the  process  of  digestion,  as  we  have 
seen,  changes  the  chemical  nature  of  the  food. 
The  food,  as  the  result  of  chemical  change,  has 
become  soluble,  and  after  being 
dissolved  it  is  dialyzable — i.  e., 
capable  of  osmosis.  After  di- 
gestion, therefore,  the  food  is 
dissolved  in  the  liquids  in  the 
stomach  and  intestine,  and  is  in 
proper  condition  for  dialysis. 

Furthermore,  the  structure  of 
the  intestine  is  such  as  to  pro- 
duce conditions  adapted  for 
dialysis.  This  can  be  under- 
stood from  Fig.  3,  which  repre- 
sents diagrainmatically  a cross 
section  through  the  intestinal 
wall.  Within  the  intestinal  wall, 
at  A , is  the  food  mass  in  solu- 
tion. At  B are  shown  little 
projections  of  the  intestinal 
wall,  called  villi , extending  into 
this  food  and  covered  by  a mem- 
brane. One  of  these  villi  is 
shown  more  highly  magnified 
in  Fig.  4,  in  which  B shows  this 
membrane.  Inside  of  these 
villi  are  blood-vessels,  C,  and  it 
will  be  thus  seen  that  the  mem- 


Fig.  2. — In  the  bladder 
A is  a sugar  solu- 
tion. In  the  vessel 
B is  pure  water. 
Sugar  passes  out 
and  water  into  the 
bladder  until  it 
rises  in  the  tube 
to  a. 


brane,  By  separates  two  liquids, 
one  containing  the  dissolved  food  outside  the  villus, 
and  the  other  containing  blood  inside  the  villus. 
Here  are  proper  conditions  for  osmosis,  and  this 
process  of  dialysis  will  take  place  whenever  the 


32 


THE  STORY  OF  THE  LIVING  MACHINE. 


intestinal  contents  holds  more  dialyzable  material 
than  the  blood.  Under  these  conditions,  which 

will  always  occur 
after  food  has  been 
digested  by  the  di- 
gestive juices,  the 
food  will  begin  to 
pass  through  this 
membranous  wall  of 
the  intestine  into  the 
blood  under  the  in- 
fluence of  the  physi- 
cal force  of  osmosis. 
Thus  the  primary 
factor  in  food  absorp- 
tion is  a physical  one. 

We  must  notice, 
however,  that  the 
physical  force  of  os- 
mosis is  not  the  only 
factor  concerned  in 
absorption.  In  the 
first  place,  it  is  found 
that  the  food  during  its  passage  through  the  intes- 
tinal wall,  or  shortly  afterwards,  undergoesa  further 
change,  so  that  by  the  time  it  has  fairly  reached 
the  blood  it  has  again  changed  its  chemical  nature. 
These  changes  are,  however,  of  a chemical  nature, 
and,  while  we  do  not  yet  know  very  much  about 
them,  they  are  of  the  same  sort  as  those  of  diges- 
tion, and  involve  probably  nothing  more  than 
chemical  processes. 

Secondly,  we  notice  that  there  is  one  phase  of 
absorption  which  is  still  obscure.  Part  of  the  food 
is  composed  of  fat,  and  this  fat,  as  the  result  of  di- 
gestion, is  mechanically  broken  up  into  extremely 


Fig.  3. — Diagram  of  the  intestinal 
walls.  A , lumen  of  intestine 
filled  with  digested  food.  B , 
villi,  containing  blood-vessels. 
C , larger  blood  vessel,  which 
carries  blood  with  absorbed  food 
away  from  .the  intestine. 


IS  THE  BODY  A MACHINE  ? 


33 


minute  droplets.  Although  these  droplets  are  of 
microscopic  size  they  are  not  actually  in  solution, 
and  therefore  not  subject  to  the  force  of  osmosis 
which  only  affects  solutions.  The  osmotic  force 
will  not  force  fat  drops  through  membranes,  and 


processes  which  the  membrane  B in  Fig.  4.  The  free 
, surface  is  at  a;  / shows  fat  droplets  in 

tliey  tnrust  out,  process  of  passage  through  the  cells, 
and  then  pass 

them  through  their  own  bodies  to  excrete  them 
on  their  inner  surface  into  the  blood-vessels. 
Fig.  5 shows  a few  of  these  living  bits  of  the 
membrane,  each  containing  several  such  fat  drop- 
lets. This  fat  absorption  thus  appears  to  be  a 


34  THE  story  of  the  living  machine. 

vital  process,  and  not  one  simply  controlled  by 
physical  forces  like  osmosis.  Here  our  explan- 
ation runs  against  what  we  call  vital  power  of 
the  ultimate  elements  of  the  body.  The  consider- 
ation of  this  vital  feature  we  must,  of  co-urse, 
investigate  further;  but  this  will  be  done  later. 
At  present  our  purpose  is  a general  comparison 
of  the  body  and  a machine,  and  we  may  for  a 
little  postpone  the  consideration  of  this  vital 
phenomenon. 

Circulation. — The  next  piece  of  mechanism  for 
us  to  consider  in  this  machine  is  the  device  for  dis- 
tributing this  fuel  to  the  various  parts  of  the  ma- 
chine where  it  is  to  be  used  as  a source  of  energy, 
corresponding  in  a sense  to  the  fireman  of  a loco- 
motive. This  mechanism  we  call  the  circulatory 
system.  It  consists  of  a series  of  tubes,  or  blood- 
vessels, running  to  every  part  of  the  body  and 
supplying  every  bit  of  tissue.  Within  the  tubes  is 
the  blood,  which,  from  its  liquid  nature,  is  easily 
forced  around  the  body  through  the  tubes.  At 
the  centre  of  the  system  is  a pump  which  keeps 
the  blood  in  motion.  The  tubes  form  a closed 
system,  such  that  the  pump,  or  heart,  may  suck 
the  blood  in  from  one  side  to  force  it  out  into  the 
tubes  on  the  other  side  ; and  the  blood,  after  pass- 
ing over  the  body  in  this  closed  set  of  tubes,  is 
finally  brought  back  again  to  be  forced  once  more 
over  the  same  path.  As  this  blood  is  carried 
around  the  body  it  conveys  from  one  part  of  the 
machine  to  another  all  material  that  needs  dis- 
tribution. While  in  the  intestine,  as  already  no- 
ticed (Fig.  3),  it  receives  the  food,  and  now  this 
food  is  carried  by  the  circulation  to  the  muscles 
or  the  other  organs  that  need  it.  While  in  the 
lungs  the  blood  receives  oxygen,  and  this  oxygen 


IS  THE  BODY  A MACHINE? 


35 


is  then  carried  to  those  parts  of  the  body  that 
need  it.  The  circulatory  system  is  thus  simply  a 
medium  by  which  each  part  of  the  machine  may 
receive  its  proper  share  of  the  supplies  needed 
for  its  action. 

Now  in  this  circulation  we  have  again  to  do 
with  chemical  and  physical  forces.  All  of  its  gen- 
eral phenomena  are  based  upon  purely  mechanical 
principles.  The  action  of  the  heart — leaving  out 
of  consideration  for  a moment  its  muscular  power 
— is  that  of  a simple  pump.  It  is  provided  with 
valves  whose  action  is  as  simple  and  as  easy  to 
understand  as  those  of  any  water  pump.  By  the 
action  of  these  valves  the  blood  is  kept  circulating 
in  one  direction.  The  blood-vessels  are  elastic, 
and  the  study  of  the  effect  of  a liquid  pumped 
rhythmically  into  elastic  tubes  explains  with  sim- 
plicity the  various  phenomena  associated  with  the 
circulation.  For  example,  the  rhythmically  con- 
tracting heart  forces  a small  quantity  of  blood 
into  the  arteries  at  short  intervals.  These  tubes 
are  large  near  the  heart,  but  smaller  at  their  ends, 
where  they  flow  into  the  veins,  so  that  the  blood 
does  not  flow  out  into  the  veins  so  readily  as  it 
flows  in  from  the  heart.  The  jet  of  blood  that  is 
sent  in  with  every  beat  of  the  heart  slightly 
stretches  the  artery,  and  the  tension  thus  produced 
causes  the  blood  to  continue  to  flow  between  the 
beats.  But  the  heart  continues  beating,  and  there 
is  an  accumulation  of  the  blood  in  the  arteries  un- 
til it  exists  under  some  pressure — a pressure  suffi- 
cient to  force  it  rapidly  through  the  small  ends  of 
the  arteries  into  the  veins.  After  passing  into  the 
veins  the  pressure  is  at  once  removed,  since  the 
veins  are  larger  than  the  arteries,  and  there  is  no 
resistance  to  the  flow  of  the  blood.  Hence  the 


36  THE  STORY  OF  THE  LIVING  MACHINE. 

blood  in  the  arteries  is  under  pressure,  while 
there  is  little  or  no  pressure  in  the  veins.  Into 
the  details  of  this  matter  we  need  not  go,  but  this 
will  be  sufficient  to  indicate  that  the  whole  pro- 
cess is  a mechanical  one. 

We  must  not  fail  to  see,  however,  that  in  this 
problem  of  circulation  there  are  two  points  at 
least  where  once  more  we  meet  with  that  class  of 
phenomena  which  we  still  call  vital.  The  beating 
of  the  heart  is  the  first  of  these,  for  this  is  active 
muscular  power.  The  second  is  a contraction  of 
the  smaller  blood-vessels  which  regulates  the  blood 
supply.  Both  of  these  phenomena  are  phases  of 
muscular  activity,  and  will  be 
included  under  the  discussion 
of  other  similar  phenomena 
later. 

We  next  notice  that  not 
only  is  the  distribution  of  the 
blood  explained  upon  me- 
chanical principles,  but  the 
supplying  of  the  active  parts 
of  the  body  with  food  is  in 
the  same  way  intelligible. 
As  we  have  seen,  the  blood 
coming  from  the  intestine 
contains  the  food  material 
received  from  the  digested 
food.  Now  when  this  blood 
in  its  circulation  flows  through 
the  active  tissues — for  in- 
stance, the  muscles — it  is 
again  placed  under  conditions 
where  osmosis  is  sure  to  oc- 
cur. In  the  muscles  the  thin-walled  blood-vessels 
are  surrounded  and  bathed  by  a liquid  called  lymph. 


Fig.  6. — A bit  of  muscle 
with  its  blood-vessels : 
a , the  muscle  fibres  ; b , 
the  minute  blood-ves- 
sels. The  fibres  and 
vessels  are  bathed  in 
lymph  (not  shown  in 
the  figure',  and  food 
material  passesthrough 
the  walls  of  the  blood- 
vessels into  this  lymph. 


IS  THE  BODY  A MACHINE?  37 

Figure  6 shows  a bit  of  muscle  tissue,  with  its 
blood-vessels,  which  are  surrounded  by  lymph. 
The  lymph,  which  is  not  shown,  fills  all  the  space 
outside  the  blood-vessels,  thus  bathing  both 
muscles  and  blood-vessels.  Here  again  we  have 
a membrane  (i.  e.,  the  wall  of  the  blood-vessel) 
separating  two  liquids,  and  since  the  lymph  is  of 
a different  composition  from  the  blood,  dialysis 
between  them  is  sure  to  occur,  and  the  materials 
which  passed  into  the  blood  in  the  intestine 
through  the  influence  of  the  osmotic  force,  now 
pass  out  into  the  lymph  under  the  influence  of  the 
same  force.  The  food  is  thus  brought  into  the 
lymph  ; and  since  the  lymph  lies  in  actual  contact 
with  the  living  muscle  fibres,  these  fibres  are  now 
able  to  take  directly  from  the  lymph  the  material' 
needed  for  their  use.  The  power  which  enables 
the  muscle  fibre  to  take  the  material  it  needs,, 
discarding  the  rest,  is,  again,  one  of  the  vital  pro- 
cesses which  we  defer  for  a moment. 

Respiration. — Pursuing  the  same  line  of  study, 
we  turn  for  a moment  to  the  relation  of  the  circu- 
latory system  to  the  function  of  supplying  the  body 
with  oxygen  gas.  Oxygen  is  absolutely  needed 
to  carry  on  the  functions  of  life;  for  these,  like 
those  of  the  engine,  are  based  upon  the  oxidation 
of  the  fuel.  The  oxygen  is  derived  from  the  air 
in  the  simplest  manner.  _ During  its  circulation 
the  blood  is  brought  for  a fraction  of  a second 
into  practical  contact  with  air.  This  occurs  in  the 
lungs,  where  there  are  great  numbers  of  air  cells,  in 
the  walls  of  which  the  blood-vessels  are  distrib- 
uted in  great  profusion.  While  the  blood  is  in 
these  vessels  it  is  not  indeed  in  actual  contact 
with  the  air,  but  is  separated  from  it  by  only  a 
very  thin  membrane — so  thin  that  it  forms  no  hin- 


38  THE  STORY  OF  THE  LIVING  MACHINE. 


drance  to  the  interchange  of  gases.  These  air- 
cells  are  kept  filled  with  air  by  simple  muscular 
action.  By  the  contraction  of  the  muscles  of  the 
thorax  the  thoracic  cavity  is  enlarged,  and  as  a 
result  air  is  sucked  in  in  exactly  the  same  way 
that  it  is  sucked  into  a pair  of  bellows  when  ex- 
panded. Then  the  contraction  of  another  set  of 
muscles  decreases  the  size  of  the  thoracic  cavity, 
and  the  air  is  squeezed  out  again.  The  action  is 
just  as  truly  mechanical  as  is  that  of  the  black- 
smith’s bellows. 

The  relation  of  the  air  to  the  blood  is  just  as 
simple.  In  the  blood  there  are  various  chemical 
ingredients,  among  which  is  one  known  as  haemo- 
globin. It  does  not  concern  us  at  present  to  ask 
where  this  material  comes  from,  since  this  ques- 
tion is  part  of  the  broader  question,  the  origin 
of  the  machine,  to  be  discussed  in  the  second 
part  of  this  work.  The  haemoglobin  is  a normal 
constituent  of  the  blood,  and,  being  red  in  colour, 
gives  the  red  colour  to  the  blood.  This  haemo- 
globin has  peculiar  relations  to  oxygen.  It  can 
be  separated  from  the  blood  and  experimented 
upon  by  the  chemist  in  his  laboratory.  It  is  found 
that  when  haemoglobin  is  brought  in  contact  with 
oxygen,  under  sufficient  pressure  it  will  form  a 
chemical  union  with  it.  This  chemical  union  is, 
however,  what  the  chemist  calls  a loose  combina- 
tion, since  it  is  readily  broken  up.  If  the  oxygen 
is  above  a certain  rather  low  pressure,  the  union 
will  take  place  ; while  if  the  pressure  be  below  this 
point  the  union  is  at  once  destroyed,  and  the  oxy- 
gen leaves  the  haemoglobin  to  become  free.  All 
of  this  is  a purely  chemical  matter,  and  can  be 
demonstrated  at  will  in  a test  tube  in  the  labora- 
tory. But  this  union  and  disassociation  is  just 


IS  THE  BODY  A MACHINE  ? 


39 


what  occurs  as  the  foundation  of  respiration.  The 
blood  coming  to  the  lungs  contains  haemoglobin, 
and  since  the  oxygen  pressure  in  the  air  is  quite 
high,  this  haemoglobin  unites  at  once  with  a quan- 
tity of  oxygen  while  the  blood  is  flowing  through 
the  air-vessels.  The  blood  is  then  carried  off  in 
the  circulation  to  the  active  tissues  like  the  mus- 
cles. These  tissues  are  constantly  using  oxygen 
to  carry  on  their  life  processes,  and  consequently 
at  all  times  use  up  about  all  the  oxygen  within 
their  reach.  The  result  is  that  in  these  tissues 
the  oxygen  pressure  is  very  low,  and  when  the 
oxygen-laden  haemoglobin  reaches  them  the  as- 
sociation of  the  haemoglobin  with  oxygen  is  at 
once  broken  up  and  the  oxygen  set  free  in  the 
tissue.  It  passes  at  once  to  the  lymph,  from  which 
the  active  tissues  seize  it  for  the  purpose  of  carry- 
ing on  the  oxidizing  processes  of  the  body.  This 
whole  matter  of  supplying  the  body  with  oxygen 
is  thus  fundamentally  a chemical  one,  controlled 
by  chemical  laws. 

Removal  of  Waste . — The  next  step  in  this  life 
process  is  one  of  difficulty.  After  the  food  and 
oxygen  have  reached  the  tissues  it  is  seized  by 
the  living  cell.  The  food  material  is  now  oxidized 
by  the  oxygen,  and  its  latent  energy  is  liberated, 
and  appears  in  the  form  of  motion  or  heat  or 
some  other  vital  function.  Herein  is  the  really 
mysterious  part  of  the  life  process;  but  for  the 
present  we  will  overlook  the  mystery  of  this  action, 
and  consider  the  results  from  a purely  material 
standpoint. 

In  a steam  engine  the  fundamental  process  by 
which  the  latent  energy  of  the  fuel  is  liberated  is 
that  of  oxidation.  The  oxygen  of  the  air  unites 
with  the  chemical  elements  of  the  fuel,  and  breaks 

4 


40  THE  STORY  OF  THE  LIVING  MACHINE. 


up  that  fuel  into  simple  compounds — which  may  be 
chieflyconsideredas  three — carbonic  dioxide(C02), 
water  (H20),  and  ash.  The  energy  contained  in 
the  original  compound  can  not  be  held  by  these 
simpler  bodies,  and  it  therefore  escapes  as  heat. 
Just  the  same  process,  with  of  course  difference 
in  details,  is  found  in  the  living  machine.  The 
food,  after  reaching  the  living  cell,  is  united  with 
the  oxygen,  and,  so  far  as  chemical  results  are  con- 
cerned, the  process  is  much  the  same  as  if  it  oc- 
curred outside  the  body.  The  food  is  broken  into 
simpler  compounds  and  the  contained  energy  is 
liberated.  The  energy  is,  by  the  mechanism  of  the 
machine,  changed  into  motion  or  nervous  impulse, 
etc.  The  food  is  broken  into  simple  compounds, 
which  are  chiefly  carbonic  dioxide,  water,  and  ash; 
the  ash  being,  however,  quite  different  from  the 
ash  obtained  from  burning  coal.  Now  the  engine 
must  have  its  chimney  to  remove  the  gases  and 
vapours  (the  C02  and  H20)  and  its  ashpit  for  the 
ashes.  In  the  same  way  the  living  machine  has 
its  excretory  system  for  removing  wastes.  In 
the  removal  of  the  carbonic  acid  and  water  we 
have  to  do  once  more  with  the  respiratory  sys- 
tem, and  the  process  is  simply  a repetition  of  the 
story  of  gas  diffusion,  chemical  union,  and  osmo- 
sis. It  is  sufficient  here  to  say  that  the  process  is 
just  as  simple  and  as  easily  explained  as  those  al- 
ready described.  The  elimination  of  these  wastes 
is  simply  a problem  of  chemistry  and  mechanics. 

In  the  removal  of  the  ash,  however,  we  have 
something  mo/e,  for  here  again  we  are  brought 
up  against  the  vital  action  of  the  cell.  This  ash 
takes  chiefly  the  form  of  a compound  known  as 
urea,  which  finds  its  way  into  the  general  circula- 
tory system.  From  the  blood  it  is  finally  removed 


IS  THE  BODY  A MACHINE  ? 


41 


by  the  kidneys.  In  the  kidneys  are  a large  num- 
ber of  bits  of  living  matter  (kidney  cells),  which 
have  the  power  of  seizing  hold  of  the  urea  as  the 
blood  is  flowing  over  them,  and  after  thus  taking 
it  out  of  the  blood  they  deposit  it  in  a series  of 
tubes  which  lead  to  the  bladder  and  hence  to  the 
exterior.  The  bringing  of  this  ash  to  the  kidney 
cell  is  a mechanical  matter,  based  simply  upon  the 
flow  of  the  blood.  The  seizing  of  the  urea  by 
the  kidney  cell  is  a vital  phenomenon  which  we 
must  waive  for  the  moment. 

Up  to  this  point  in  the  analysis  there  has  been 
no  difficulty,  and  no  one  can  fail  to  agree  with 
the  conclusions.  The  position  we  reach  is  as  fol- 
lows: So  far  as  relates  to  the  general  problems  of 
energy  in  the  universe  the  body  is  a machine.  It 
neither  creates  nor  destroys  energy,  but  simply 
transforms  one  form  into  another.  In  attempt- 
ing to  explain  the  action  of  the  machine,  we  find 
that  for  the  functions  thus  far  considered  (some- 
times called  the  vegetative  functions)  the  laws 
of  chemistry  and  physics  furnish  adequate  ex- 
planation. 

We  must  now  look  a little  further,  and  question 
some  of  the  functions  the  mechanical  nature  of 
which  is  less  obvious.  The  whole  operation  thus 
far  described  is  under  the  control  of  the  nervous 
system,  which  acts  somewhat  like  the  engineer  of 
an  engine.  Can  this  phase  of  living  activity  be 
included  within  the  conception  of  the  body  as  a 
machine  ? 

Nervous  System . — When  we  come  to  try  to  apply 
mechanical  principles  to  the  nervous  system,  we 
meet  with  what  seems  at  first  to  be  no  thorough- 
fare. While  dealing  with  the  grosser  questions  of 
chemical  compounds,  heat,  and  motion,  there  is 


42  THE  STORY  OF  THE  LIVING  MACHINE. 


little  difficulty  in  applying  natural  laws  to  the  ex- 
planation of  living  phenomena.  But  the  problem 
with  the  nervous  system  is  very  different.  It  is 
only  to-day  that  we  are  finding  that  the  problem 
is  open  to  study,  to  say  nothing  of  solution.  It 
is  true  that  mental  and  other  nervous  phenomena 
have  been  studied  for  a long  time,  but  this  study 
has  been  simply  the  study  of  these  phenomena  by 
themselves  without  a thought  of  their  correlation 
with  other  phenomena  of  nature.  It  is  a matter 
of  quite  recent  conception  that  nervous  phenom- 
ena have  any  direct  relation  to  the  other  realms  of 
nature. 

Our  first  question  must  be  whether  we  can  find 
any  correlation  between  nervous  energy  and  other 
types  of  energy.  For  our  purpose  it  will  be  con- 
venient to  distinguish  between  the  phenomena  of 
simple  nervous  transmission  and  the  phenomena 
of  mental  activity.  The  former  are  the  simpler, 
and  offer  the  greatest  hope  of  solution.  If  we  are 
to  find  any  correlation  between  nervous  energy 
and  other  physical  energy,  we  must  do  so  by  find- 
ing some  way  of  measuring  nervous  energy  and 
comparing  it  with  the  latter.  This  has  been  very 
difficult,  for  we  have  no  way  of  measuring  a nerv- 
ous impulse  directly.  In  the  larger  experiments 
upon  the  income  and  outgo  of  the  body,  in  the 
respiration  apparatus  mentioned  above,  nervous 
phenomena  apparently  leave  no  trace.  So  far  as 
experiments  have  gone  as  yet,  there  is  no  evidence 
of  an  expenditure  of  extra  physical  energy  when 
the  nervous  system  is  in  action.  This  is  not  sur- 
prising, however,  for  this  apparatus  is  entirely  too 
coarse  to  measure  such  delicate  factors. 

That  there  is  a correlation  between  nervous 
energy  and  physical  energy  is,  however,  pretty 


IS  THE  BODY  A MACHINE? 


43 


definitely  proved  by  experiments  along  different 
lines.  The  first  step  in  this  direction  was  to  find 
that  a nervous  stimulus  can  be  measured  at  least 
indirectly.  When  the  nerve  is  stimulated  there 
passes  from  one  end  to  the  other  an  impulse,  and 
the  rapidity  with  which  it  travels  can  be  accurately 
measured.  When  such  an  impulse  reaches  the 
brain  it  may  give  rise  to  a conscious  sensation, 
and  a somewhat  definite  estimation  can  be  made 
of  the  amount  of  time  required  for  this.  The 
periods  are  very  short,  of  course,  but  they  are 
not  instantaneous.  The  nervous  impulse,  can  be 
studied  in  still  other  ways.  We  find  that  the  im- 
pulse can  be  started  by  ordinary  forms  of  energy. 
A mechanical  shock,  a chemical  or  an  electrical 
shock  will  develop  nervous  energy.  Now  these 
are  ordinary  forms  of  physical  energy,  and  if,  when 
they  are  applied  to  a nerve,  they  give  rise  to  a 
nervous  stimulus,  the  inference  is  certainly  a le- 
gitimate one  that  the  nerve  is  simply  a bit  of  ma- 
chinery adapted  to  the  conversion  of  certain  kinds 
of  physical  energy  into  nervous  energy.  If  this 
is  the  case,  then  it  is  necessary  to  regard  nervous 
energy  as  correlated  with  other  forms  of  energy. 

Other  facts  point  in  the  same  direction.  Not 
only  can  the  nervous  stimulus  be  developed  by 
an  electric  shock,  but  the  strength  of  the  stimulus 
is  within  certain  limits  proportional  to  the  strength 
of  the  shock  which  produces  it.  Again,  not  only 
is  it  found  that  an  electrical  shock  can  develop 
a nervous  stimulus,  but  conversely  a nervous 
stimulus  develops  electrical  energy.  In  ordinary 
nerves,  even  when  not  active,  slight  electric  cur- 
rents can  be  detected.  They  are  extremely  slight, 
and  require  the  most  delicate  instruments  for 
their  detection.  Now  when  a nerve  is  stimulated 


44  THE  story  of  the  living  machine. 

these  currents  are  immediately  affected  in  such  a 
way  that  under  proper  conditions  they  are  in- 
creased in  intensity.  The  increase  is  sufficient  to 
make  itself  easily  seen  by  the  motion  of  a galva- 
nometer. The  motion  of  the  galvanometer  under 
these  conditions  gives  a ready  means  of  studying 
the  character  of  the  nervous  impulse.  By  its  use 
it  can  be  determined  that  the  nerve  impulse  travels 
along  the  nerve  like  a wave,  and  we  can  approxi- 
mately determine  the  length  and  shape  of  the 
wave  and  its  relative  height  at  various  points. 

Now  what  is  the  significance  of  all  these  facts 
for  our  discussion?  Together  they  point  clearly 
to  the  conclusion  that  nervous  energy  is  corre- 
lated with  other  forms  of  physical  energy.  Since 
the  nervous  stimulus  is  started  by  other  forms  of 
energy,  and  since  it  can,  in  turn,  modify  ordinary 
forms  of  energy,  we  can  not  avoid  the  conclusion 
that  the  nervous  impulse  is  only  a special  form  of 
energy  developed  within  the  nerve.  It  is  a form 
of  wave  motion  peculiar  to  the  nerve  substance, 
but  correlated  with  and  developed  from  other 
types  of  energy.  This,  of  course,  makes  the  nerve 
simply  a bit  of  machinery. 

If  this  conclusion  is  true,  the  development  of 
a nerve  impulse  would  mean  that  a certain  portion 
of  food  is  broken  to  pieces  in  the  body  to  liberate 
energy,  and  this  should  be  accompanied  by  an 
elimination  of  carbonic  dioxide  and  heat.  This  is 
easily  shown  to  be  true  of  muscle  action.  When 
we  remove  a muscle  from  the  body  it  may  remain 
capable  of  contracting  for  some  time.  By  study- 
ing it  under  these  conditions  we  find  that  it  gives 
rise  to  carbonic  dioxide  and  other  substances,  and 
liberates  heat  whenever  it  contracts.  As  already 
noticed,  in  the  respiration  experiments,  whenever 


IS  THE  BODY  A MACHINE?  45 

the  individual  experimented  upon  makes  any  mo- 
tions, there  is  an  accompanying  elimination  of 
waste  products  and  a development  of  heat.  But 
this  does  not  appear  to  be  demonstrable  for  the 
actions  of  the  nervous  system.  Although  very 
careful  experiments  have  been  made,  it  has  as  yet 
been  found  impossible  to  detect  any  rise  in  tem- 
perature when  a nerve  impulse  is  passing  through 
a nerve,  nor  is  there  any  demonstrable  excretion 
of  waste  products.  This  would  be  a serious  objec- 
tion to  the  conception  of  the  nerve  as  a machine 
were  it  not  for  the  fact  that  the  nerve  is  so  small 
that  the  total  sum  of  its  nervous  energy  must  be 
very  slight.  The  total  energy  of  this  minute  ma- 
chine is  so  slight  that  it  can  not  be  detected  by 
our  comparatively  rough  instruments  of  measure- 
ment. 

In  short,  all  evidence  goes  to  show  that  the 
nerve  impulse  is  a form  of  motion,  and  hence  of 
energy,  correlated  with  other  forms  of  physical 
energy.  The  nerve  is,  however,  a very  delicate 
machine,  and  its  total  amount  of  energy  is  very 
small.  A tiny  watch  is  a more  delicate  machine 
than  a water-wheel,  and  its  actions  are  more  de- 
pendent upon  the  accuracy  of  its  adjustment. 
The  water-wheel  may  be  made  very  coarse  and 
yet  be  perfectly  efficacious,  while  the  watch  must 
be  fashioned  with  extreme  delicacy.  Yet  the  water- 
wheel transforms  vastly  more  energy  than  the 
watch.  It  may  drive  the  many  machines  in  a fac- 
tory, while  the  watch  can  do  no  more  than  move 
itself.  But  who  can  doubt  that  the  watch,  as  well 
as  the  water-wheel,  is  governed  by  the  law  of  the 
correlation  of  forces?  So  the  nervous  system  of 
the  living  machine  is  delicately  adjusted  and  eas- 
ily put  out  of  order,  and  its  action  involves  only 


46  THE  STORY  OF  THE  LIVING  MACHINE. 

a small  amount  of  energy ; but  it  is  just  as  truly 
subject  to  the  law  of  the  conservation  of  energy 
as  is  the  more  massive  muscle. 

Sensations. — Pursuing  this  subject  further,  we 
next  notice  that  it  is  possible  to  trace  a connection 
between  physical  energy  and  sensations . Sensa- 
tions are  excited  by  certain  external  forms  of  mo- 
tion. The  living  machine  has,  for  example,  one 
piece  of  apparatus  capable  of  being  affected  by 
rapidly  vibrating  waves  of  air.  This  bit  of  the 
machine  we  call  the  ear.  It  is  made  of  parts  deli- 
cately adjusted,  so  that  vibrating  waves  of  air  set 
them  in  motion,  and  their  motion  starts  a nervous 
stimulus  travelling  along  the  auditory  nerve.  As 
a result  this  apparatus  will  be  set  in  motion,  and 
an  impulse  sent  along  the  auditory  nerve  when- 
ever that  external  type  of  motion  which  we  call 
sound  strikes  the  ear.  In  other  words,  the  ear  is 
a piece  of  apparatus  for  changing  air  vibrations 
into  nervous  stimulation,  and  is  therefore  a ma- 
chine. Apparently  the  material  in  the  ear  is  like 
a bit  of  gunpowder,  capable  of  being  exploded  by 
certain  kinds  of  external  excitation  ; but  neither 
the  gunpowder  nor  the  material  in  the  ear  de- 
velops any  energy  other  than  that  in  it  at  the  out- 
set. In  the  same  way  the  optic  nerve  has,  at  its 
end,  a bit  of  mechanism  readily  excited  by  light 
vibrations  of  the  ether,  and  hence  the  optic  nerve 
will  always  be  excited  when  ether  vibrations 
chance  to  have  an  opportunity  of  setting  the  op- 
tic machinery  in  motion.  And  so  on  with  the  other 
senses.  Each  sensory  nerve  has,  at  its  end,  a bit 
of  machinery  designed  for  the  transformation  of 
certain  kinds  of  external  energy  into  nervous  en- 
ergy,  just  as  a dynamo  is  a machine  for  trans- 
forming motion  into  electricity.  If  the  machine  is 


IS  THE  BODY  A MACHINE? 


47 


broken,  the  external  force  has  no  longer  any  power 
of  acting  upon  it,  and  the  individual  becomes  deaf 
or  blind. 

Mental  Phenomena . — Thus  far  in  our  analysis 
we  need  not  hesitate  in  recognizing  a correlation 
between  physical  and  nervous  energy.  Even 
though  nervous  energy  is  very  subtle  and  only 
affects  our  instruments  of  measurements  under 
exceptional  conditions,  the  fact  that  nervous 
forces  are  excited  by  physical  forces,  and  are  them- 
selves directly  measurable,  indicates  that  they  are 
correlated  with  physical  forces.  Up  to  this  point, 
then,  we  may  confidently  say  that  the  nervous 
system  is  part  of  the  machine. 

But  when  we  turn  to  the  more  obscure  parts  of 
the  nervous  phenomena,  those  which  we  commonly 
call  mental,  we  find  ourselves  obliged  to  stop  ab- 
ruptly. We  may  trace  the  external  force  to  the 
sensory  organ,  we  may  trace  this  force  into  a nerv- 
ous stimulus,  and  may  follow  this  stimulus  to  the 
brain  as  a wave  motion,  and  therefore  as  a form 
of  physical  energy.  But  there  we  must  stop.  We 
have  no  idea  of  how  the  nervous  impulse  is  con- 
verted into  a sensation.  The  mental  side  of  the 
sensation  appears  to  stand  in  a category  by  itself, 
and  we  can  not  look  upon  it  as  a form  of  energy. 
It  is  true  that  many  brave  attempts  have  been 
made  to  associate  the  two.  Sensations  can  be 
measured  as  to  intensity,  and  the  intensity  of  a 
sensation  is  to  a certain  extent  dependent  upon 
the  intensity  of  the  stimulus  exciting  it.  The 
mental  sensation  is  undoubtedly  excited  by  the 
physical  wave  of  nervous  impulse.  In  the  growth 
of  the  individual  the  development  of  its  mental 
powers  are  found  to  be  parallel  to  the  development 
of  its  nerves  and  brain — a fact  which,  of  course, 


48  THE  STORY  OF  THE  LIVING  MACHINE. 

proves  that  mental  power  is  dependent  upon  brain 
structure.  Further,  it  is  found  that  certain  visible 
changes  occur  in  certain  parts  of  the  brain — the 
brain  cells — when  they  are  excited  into  mental  ac- 
tivity. Such  series  of  facts  point  to  an  association 
between  the  mental  side  of  sensations  and  physical 
structure  of  the  machine.  But  they  do  not  prove 
any  correlation  between  them.  The  unlikeness  of 
mental  and  physical  phenomena  is  so  absolute 
that  we  must  hesitate  about  drawing  any  connec- 
tion between  them.  It  is  impossible  to  conceive 
the  mental  side  of  a sensation  as  a form  of  wave 
motion.  If,  further,  we  take  into  consideration  the 
other  phenomena  associated  with  the  nervous  sys- 
tem, the  more  distinctly  mental  processes,  we  have 
absolutely  no  data  for  any  comparison.  We  can 
not  imagine  thought  measured  by  units,  and  until 
we  can  conceive  of  such  measurement  we  can  get 
no  meaning  from  any  attempt  to  find  a correlation 
between  mental  and  physical  phenomena.  It  is 
true  that  certain  psychologists  have  tried  to  build 
up  a conception  of  the  physical  nature  of  mind ; 
but  their  attempts  have  chiefly  resulted  in  building 
up  a conception  of  the  physical  nature  of  the  brain, 
and  then  ignoring  the  radical  chasm  that  exists 
between  mind  and  matter.  The  possibility  of  de- 
scribing a complex  brain  as  growing  parallel  to  the 
growth  of  a complex  mind  has  been  regarded  as 
equivalent  to  proving  their  identity.  All  attempts 
in  this  direction  thus  far  have  simply  ignored  the 
fact  that  the  stimulation  of  a nerve,  a purely  phys- 
ical process,  is  not  the  same  thing  as  a mental  ac- 
tion. What  the  future  may  disclose  it  is  hazardous 
to  say,  but  at  present  the  mental  side  of  the  liv- 
ing machine  has  not  been  included  within  the  con- 
ception of  the  mechanical  nature  of  the  organism. 


IS  THE  BODY  A MACHINE? 


49 


The  Living  Body  is  a Machine. — Reviewing  the 
subject  up  to  this  point,  what  must  be  our  verdict 
as  to  our  ability  to  understand  the  running  of  the 
living  machine?  In  the  first  place,  we  are  jus- 
tified in  regarding  the  body  as  a machine,  since, 
so  far  as  concerns  its  relations  to  energy,  it  is  sim- 
ply a piece  of  mechanism — complicated,  indeed, 
beyond  any  other  machine,  but  still  a machine  for 
changing  one  kind  of  energy  into  another.  It 
receives  the  energy  in  the  form  of  chemical  com- 
position and  converts  it  into  heat,  motion,  nervous 
wave  motion,  etc.  All  of  this  is  sure  enough. 
Whether  other  forms  of  nervous  and  mental  ac- 
tivity can  be  placed  under  the  same  category,  or 
whether  these  must  be  regarded  as  belonging  to 
a realm  by  themselves  and  outside  of  the  scope 
of  energy  in  the  physical  sense,  can  not  perhaps 
be  yet  definitely  decided.  We  can  simply  say 
that  as  yet  no  one  has  been  able  even  to  conceive 
how  thought  can  be  commensurate  with  physical 
energy.  The  utter  unlikeness , of  thought  and 
wave  motion  of  any  kind  leads  us  at  present  to 
feel  that  on  the  side  of  mentality  the  comparison 
of  the  body  with  a machine  fails  of  being  com- 
plete. 

In  regard  to  the  second  half  of  the  question, 
whether  natural  forces  are  adequate  to  explain 
the  running  of  the  machine,  we  have  again  been 
able  to  reach  a satisfactory  positive  answer.  Di- 
gestion, assimilation,  circulation,  respiration,  ex- 
cretion, the  principal  categories  of  physiological 
action,  and  at  least  certain  phases  of  the  action 
of  the  nervous  system  are  readily  understood  as 
controlled  by  the  action  of  chemical  and  physical 
forces.  In  the  accomplishment  of  these  actions 
there  is  no  need  for  the  supposition  of  any  force 


50  THE  STORY  OF  THE  LIVING  MACHINE. 

other  than  those  which  are  at  our  command  in 
the  scientific  laboratory. 

The  Living  Machine  Constructive  as  well  as 
Destructive. — In  one  respect  the  living  machine 
differs  from  all  others.  The  action  of  all  other 
machines  results  in  the  destruction  of  organized 
material,  and  thus  in  a degradation  of  matter.  For 
example,  a steam  engine  receives  coal,  a substance 
of  high  chemical  composition,  and  breaks  it  into 
more  simple  compounds,  in  this  way  liberating  its 
stored  energy.  Now  if  we  examine  all  forms  of 
artificial  machines,  we  find  in  the  same  way  that 
there  is  always  a destruction  of  compounds  of 
high  chemical  composition.  In  such  machines  it 
is  common  to  start  with  heat  as  a source  of  ener- 
gy, and  this  heat  is  always  produced  by  the  break- 
ing of  chemical  compounds  to  pieces.  In  all  chemi- 
cal processes  going  on  in  the  chemist’s  laboratory 
there  is  similarly  a destruction  of  organic  com- 
pounds. It  is  true  that  the  chemist  sometimes 
makes  complex  compounds  out  of  simpler  ones; 
but  in  order  to  do  this  he  is  obliged  to  use  heat  to 
bring  about  the  combination,  and  this  heat  is  ob- 
tained from  the  destruction  of  a much  larger 
quantity  of  high  compounds  than  he  manufactures. 
The  total  result  is  therefore  destruction  rather  than 
manufacture  of  high  compounds.  Thus  it  is  a fact, 
that  in  all  artificial  machines  and  in  all  artificial 
chemical  processes  there  is,  as  a total  result,  a deg- 
radation of  matter  toward  the  simpler  from  the 
more  complex  compounds. 

As  a result  of  the  action  of  the  living  machine, 
however,  we  have  the  opposite  process  of  construc- 
tion going  on.  All  high  chemical  compounds  are 
to  be  traced  to  living  beings  as  their  source.  When 
green  plants  grow  in  sunlight  they  take  simple 


IS  THE  BODY  A MACHINE?  51 

compounds  and  combine  them  together  to  form 
more  complex  ones  in  such  a way  that  the  total 
result  is  an  increase  of  chemical  compounds  of 
high  complexity.  In  doing  this  they  use  the 
energy  of  sunlight,  which  they  then  store  away 
in  the  compounds  formed.  They  thus  produce 
starches,  oils,  proteids,  woods,  etc.,  and  these 
stores  of  energy  now  may  be  used  by  artificial 
machines.  The  living  machine  builds  up,  other 
machines  pull  down.  The  living  machine  stores 
sunlight  in  complex  compounds,  other  machines 
take  it  out  and  use  it.  The  living  organism  is 
therefore  to  be  compared  to  a sun  engine,  which 
obtains  its  energy  directly  from  the  sun,  rather 
than  to  the  ordinary  engine.  While  this  does  not 
in  the  slightest  militate  against  the  idea  of  the 
living  body  as  a machine,  it  does  indicate  that  it 
is  a machine  of  quite  a different  character  from 
any  other,  and  has  powers  possessed  by  no  other 
machine.  Living  machines  alone  increase  the  amount 
of  chemical  compounds  of  high  complexity. 

We  must  notice,  however,  that  this  power  of 
construction  in  distinction  from  destruction,  is 
possessed  only  by  one  special  class  of  living  ma- 
chines. Green  plants  alone  can  thus  increase  the 
store  of  organic  compounds  in  the  world.  All  col- 
ourless plants  and  all  animals,  on  the  other  hand, 
live  by  destroying  these  compounds  and  using 
the  energy  thus  liberated;  in  this  respect  being 
more  like  ordinary  artificial  machines.  The  ani- 
mal does  indeed  perform  certain  constructive  op- 
erations, manufacturing  complex  material  out  of 
simpler  bodies  ; as,  for  example,  making  fats  out  of 
starches.  But  in  this  operation  it  destroys  a large 
amount  of  organic  material  to  furnish  the  energy 
for  the  construction,  so  that  the  total  result  is  a 


52  THE  STORY  OF  THE  LIVING  MACHINE. 


degradation  of  chemical  compounds  rather  than  a 
construction.  Constructive  processes,  which  in- 
crease the  amount  of  high  compounds  in  nature, 
are  confined  to  the  living  machine,  and  indeed  to 
one  special  form  of  it,  viz.,  the  green  plant.  This 
constructive  pow7er  radically  separates  the  living 
from  other  machines;  for  while  constructive  pro- 
cesses are  possible  to  the  chemist,  and  while  en- 
gines making  use  of  sunlight  are  possible,  the  liv- 
ing machine  is  the  only  machine  that  increases 
the  amount  of  high  chemical  compounds  in  the 
world. 

The  Vital  Factor. — With  all  this  explanation  of 
life  processes  it  can  not  fail  to  be  apparent  that 
we  have  not  really  reached  the  centre  of  the  prob- 
lem. We  have  explained  many  secondary  pro- 
cesses, but  the  primary  ones  are  still  unsolved. 
In  studying  digestion  we  reach  an  understanding 
of  everything  until  vTe  come  to  the  active  vital 
property  of  the  gland-cells  in  secreting.  In  study- 
ing absorption  we  understand  the  process  until 
we  come  to  what  wre  have  called  the  vital  powders 
of  the  absorptive  cells  of  the  alimentary  canal. 
The  circulation  is  intelligible  until  v7e  come  to 
the  beating  of  the  heart  and  the  contraction  of 
the  muscles  of  the  blood-vessels.  Excretion  is 
also  partly  explained,  but  here  again  wTe  finally 
must  refer  certain  processes  to  the  vital  powers 
of  active  cells.  And  thus  wherever  w*e  probe  the 
problem  w7e  find  ourselves  able  to  explain  many 
secondary  problems,  w7hile  the  fundamental  ones 
we  still  attribute  to  the  vital  properties  of  the  ac- 
tive tissues.  Why  a muscle  contracts  or  a gland 
secretes  we  have  certainly  not  yet  answered. 
The  relation  of  the  actions  to  the  general  prob- 
lems of  correlation  of  force  is  simple  enough. 


IS  THE  BODY  A MACHINE?  53 

That  a muscle  is  a machine  in  the  sense  of  our 
definition  is  beyond  question.  But  the  problem 
of  why  a muscle  acts  is  not  answered  by  showing 
that  it  derives  its  energy  from  broken  food  ma- 
terial. There  are  plainly  still  left  for  us  a num- 
ber of  fundamental  problems,  although  the  sec- 
ondary ones  are  soluble. 

What  can  we  say  in  regard  to  these  funda- 
mental vital  powers  of  the  active  tissues  ? Firstly, 
we  must  notice  that  many  of  the  processes  which 
we  now  understand  were  formerly  classed  as  vital, 
and  we  only  retain  under  this  term  those  which 
are  not  yet  explained.  This,  of  course,  suggests 
to  us  that  perhaps  we  may  some  day  find  an  ex- 
planation for  all  the  so-called  vital  powers  by  the 
application  of  simple  physical  forces.  Is  it  a fact 
that  the  only  significance  to  the  term  vital  is  that 
we  have  not  yet  been  able  to  explain  these  pro- 
cesses to  our  entire  satisfaction  ? Is  the  differ- 
ence between  what  we  have  called  the  second- 
ary processes  and  the  primary  ones  only  one  of 
degree?  Is  there  a probability 'that  the  actions 
which  we  now  call  vital  will  some  day  be  as  read- 
ily understood  as  those  which  have  already  been 
explained  ? 

Is  there  any  method  by  which  we  can  approach 
these  fundamental  problems  of  muscle  action, 
heart  beat,  gland  secretion,  etc.  ? Evidently,  if  this 
is  to  be  done,  it  must  be  by  resolving  the  body 
into  its  simple  units  and  studying  these  units.  Our 
study  thus  far  has  been  a study  of  the  machinery 
of  the  body  as  a whole;  but  we  have  found  that 
the  various  parts  of  the  machine  are  themselves 
active,  that  apart  from  the  action  of  the  general 
machine  as  a whole,  the  separate  parts  have  vital 
powers.  We  must,  therefore,  get  rid  of  this  com- 


54  THE  story  of  the  living  machine. 

plicated  machinery,  which  confuses  the  problem, 
and  see  if  we  can  find  the  fundamental  units  which 
show  these  properties,  unencumbered  by  the  sec- 
ondary machinery  which  has  hitherto  attracted  our 
attention.  We  must  turn  now  to  the  problem 
connected  with  protoplasm  and  the  living  cell, 
since  here,  if  anywhere,  can  we  find  the  life  sub- 
stance reduced  to  its  lowest  terms. 


CHAPTER  II. 

THE  CELL  AND  PROTOPLASM. 

Vital  Properties. — We  have  seen  that  the  gen- 
eral activities  of  the  body  are  intelligible  accord- 
ing to  chemical  and  mechanical  laws,  provided  we 
can  assume  as  their  foundation  the  simple  vital 
properties  of  living  phenomena.  We  must  now 
approach  closer  to  the  centre  of  the  problem,  and 
ask  whether  we  can  trace  these  fundamental  prop- 
erties to  their  source  and  find  an  explanation  of 
them. 

In  the  first  place,  what  are  these  properties? 
The  vital  powers  are  varied,  and  lie  at  the  basis 
of  every  form  of  living  activity.  When  we  free 
them  from  complications,  however,  they  may  all 
be  reduced  to  four.  These  are:  (i)  Irritability,  or 
the  property  possessed  by  living  matter  of  react- 
ing when  stimulated.  (2)  Movement,  or  the  power 
of  contracting  when  stimulated.  (3)  Metabolism, 
or  the  power  of  absorbing  extraneous  food  and  pro- 
ducing in  it  certain  chemical  changes,  which  either 
convert  it  into  more  living  tissue  or  break  it  to 
pieces  to  liberate  the  inclosed  energy.  (4)  Repro - 


THE  CELL  AND  PROTOPLASM.  55 

duction,  or  the  power  of  producing  new  individu- 
als. From  these  four  simple  vital  activities  all 
other  vital  actions  follow;  and  if  we  can  find  an 
explanation  of  these,  we  have  explained  the  living 
machine.  If  we  grant  that  certain  parts  of  the 
body  can  assimilate  food  and  multiply,  having  the 
power  of  contraction  when  irritated,  we  can  readily 
explain  the  other  functions  of  the  living  machine 
by  the  application  of  these  properties  to  the  com- 
plicated machinery  of  the  body.  But  these  prop- 
erties are  fundamental,  and  unless  we  can  grasp 
them  we  have  failed  to  reach  the  centre  of  the 
problem. 

As  we  pass  from  the  more  to  the  less  compli- 
cated animals  we  find  a gradual  simplification  of 
the  machinery  until  the  machinery  apparently  dis- 
appears. With  this  simplification  of  the  machin- 
ery we  find  the  animals  provided  with  less  varied 
powers  and  with  less  delicate  adaptations  to  con- 
ditions. But  withal  we  find  the  fundamental  powers 
of  the  living  organisms  the  same.  For  the  perform- 
ance of  these  fundamental  activities  there  is  ap- 
parently needed  no  machinery.  The  simple  types 
of  living  bodies  are  simple  in  number  of  parts,  but 
they  possess  essentially  the  same  powers  of  assimi- 
lation and  growth  that  characterize  the  higher 
forms.  It  is  evident  that  in  our  attempt  to  trace 
the  vital  properties  to  their  source  we  may  proceed 
in  two  ways.  We  may  either  direct  our  attention 
to  the  simplest  organisms  where  all  secondary  ma- 
chinery is  wanting,  or  to  the  smallest  parts  into 
which  the  tissues  of  higher  organisms  can  be  re- 
solved and  yet  retain  their  life  properties.  In 
either  way  we  may  hope  to  find  living  phenomena 
in  its  simplest  form  independent  of  secondary  ma- 
chinery. 


5 


56  THE  STORY  OF  THE  LIVING  MACHINE. 

But  the  fact  is,  when  we  turn  our  attention 
in  these  two  directions,  we  find  the  result  is  the 
same.  If  we  look  for  the  lowest  organisms  we 
find  them  among  forms  that  are  made  of  a single 
cell,  and  if  we  analyze  the  tissues  of  higher  animals 
we  find  the  ultimate  parts  to  be  cells.  Thus,  in 
either  direction,  the  study  of  the  cell  is  forced 
upon  us. 

Before  beginning  the  study  of  the  cell  it  will 
be  well  for  us  to  try  to  get  a clear  notion  of  the 
exact  nature  of  the  problems  we  are  trying  to 
solve.  We  wish  to  explain  the  activities  of  life 
phenomena  in  such  a way  as  to  make  them  intel- 
ligible through  the  application  of  natural  forces. 
That  these  processes  are  fundamentally  chemical 
ones  is  evident  enough.  A chemical  oxidation  of 
food  lies  at  the  basis  of  all  vital  activity,  and  it  is 
thus  through  the  action  of  chemical  forces  that 
the  vital  powTers  are  furnished  with  their  energy. 
But  the  real  problem  is  what  it  is  in  the  living  ma- 
chine that  controls  these  chemical  processes.  Fat 
and  starch  may  be  oxidized  in  a chemist’s  test 
tubes,  and  will  there  liberate  energy;  but  they  do 
not,  under  these  conditions,  manifest  vital  phe- 
nomena. Proteid  may  be  brought  in  contact  with 
oxygen  without  any  oxidation  occurring,  and  even 
if  it  is  oxidized  no  motion  or  assimilation  or  repro- 
duction occurs  under  ordinary  conditions.  These 
phenomena  occur  only  when  the  oxidation  takes 
place  in  the  living  machine.  Our  problem  is  then  to 
determine,  if  possible,  what  it  is  in  the  living  ma- 
chine that  regulates  the  oxidations  and  other 
changes  in  such  a way  as  to  produce  from  them 
vital  activities.  Why  is  it  that  the  oxidation  of 
starch  in  the  living  machine  gives  rise  to  motion, 
growth,  and  reproduction,  while  if  the  oxidation 


THE  CELL  AND  PROTOPLASM. 


57 


occurs  in  the  chemist’s  laboratory,  or  even  in  a bit 
of  dead  protoplasm,  it  simply  gives  rise  to  heat  ? 

One  of  the  primary  questions  to  demand  atten- 
tion in  this  search  is  whether  we  are  to  find  the 
explanation,  at  the  bottom,  a chemical  or  a mechani- 
cal one.  In  the  simplest  form  of  life  in  which  vital 
manifestations  are  found  are  we  to  attribute  these 
properties  simply  to  chemical  forces  of  the  living 
substance,  or  must  we  here  too  attribute  them  to 
the  action  of  a complicated  machinery?  This 
question  is  more  than  a formal  one.  That  it  is 
one  of  most  profound  significance  will  appear 
from  the  following  considerations  : 

Chemical  affinity  is  a well  recognized  force. 
Under  the  action  of  this  force  chemical  com- 
pounds are  produced  and  different  compounds 
formed  under  different  conditions.  The  proper- 
ties of  the  different  compounds  differ  with  their 
composition,  and  the  more  complex  are  the  com- 
pounds the  more  varied  their  properties.  Now  it 
might  be  assumed  as  an  hypothesis  that  there 
could  be  a chemical  compound  so  complex  as  to 
possess,  among  other  properties,  that  of  causing 
the  oxidation  of  food  to  occur  in  such  a way  as 
to  produce  assimilation  and  growth.  Such  a com- 
pound would,  of  course,  be  alive,  and  it  would  be 
just  as  true  that  its  power  of  assimilating  food 
would  be  one  of  its  physical  properties  as  it  is 
that  freezing  is  a physical  property  of  water.  If 
such  an  hypothesis  should  prove  to  be  the  true 
one,  then  the  problem  of  explaining  life  would 
be  a chemical  one,  for  all  vital  properties  would 
be  reducible  to  the  properties  of  a chemical  com- 
pound. It  would  then  only  be  necessary  to  show 
how  such  a compound  came  into  existence  and 
we  should  have  explained  life.  Nor  would  this 


58  THE  STORY  OF  THE  LIVING  MACHINE. 

be  a hopeless  task.  We  are  well  acquainted  with 
forces  adequate  to  the  formation  of  chemical 
compounds.  If  the  force  of  chemical  affinity  is 
adequate  under  certain  conditions  to  form  some 
compounds,  it  is  easy  to  conceive  it  as  a possi- 
bility under  other  conditions  to  produce  this 
chemical  living  substance.  Our  search  would 
need  then  to  be  for  a set  of  conditions  .under 
which  our  living  compound  could  have  been  pro- 
duced by  the  known  forces  of  chemical  affinity. 

But  suppose,  on  the  other  hand,  that  we  find 
this  simplest  bit  of  living  matter  is  not  a chemical 
compound,  but  is  in  itself  a complicated  machine. 
Suppose  that,  after  reducing  this  vital  substance 
to  its  simplest  type,  we  find  that  the  substance 
with  which  we  are  dealing  not  only  has  complex 
chemical  structure,  but  that  it  also  possesses  a 
large  number  of  structural  parts  adapted  to  each 
other  in  such  a way  as  to  work  together  in  the 
form  of  an  intricate  mechanism.  The  whole  prob- 
lem would  then  be  changed.  To  explain  such  a 
machine  we  could  no  longer  call  upon  chemical 
forces.  Chemical  affinity  is  adequate  to  the  ex- 
planation of  chemical  compounds  however  com- 
plicated, but  it  cannot  offer  any  explanation  for 
the  adaptation  of  parts  which  make  a machine. 
The  problem  of  the  origin  of  the  simplest  form  of 
life  would  then  be  no  longer  one  of  chemical  but 
one  of  mechanical  evolution.  It  is  plain  then  that 
the  question  of  whether  we  can  attribute  the  prop- 
erties of  the  simplest  type  of  life  to  chemical 
composition  or  to  mechanical  structure  is  more 
than  a formal  one. 

The  Discovery  of  Cells. — It  is  difficult  for  us 
to-day  to  have  any  adequate  idea  of  the  wonder- 
ful flood  of  light  that  was  thrown  upon  scientific 


THE  CELL  AND  PROTOPLASM. 


59 


and  philosophical  study  by  the  discoveries  which 
are  grouped  around  the  terms  cells  and  proto- 
plasm. Cells  and  protoplasm  have  become  so 
thoroughly  a part  of  modern  biology  that  we  can 
hardly  picture  to  ourselves  the  vagueness  of 
knowledge  before  these  facts  were  recognized: 
Perhaps  a somewhat  crude  comparison  will  illus- 
trate the  relation  which  the  discovery  of  cells 
had  to  the  study  of  life. 

Imagine  for  a moment,  some  intelligent  being 
located  on  the  moon  and  trying  to  study  the  phe- 
nomena on  the  earth’s  surface.  Suppose  that  he 
is  provided  with  a telescope  sufficiently  powerful 
to  disclose  moderately  large  objects  on  the  earth, 
but  not  smaller  ones.  He  would  see  cities  in 
various  parts  of  the  world  with  wide  differences  in 
appearance,  size,  and  shape.  He  would  see  rail- 
road trains  on  the  earth  rushing  to  and  fro.  He 
would  see  new  cities  arising  and  old  ones  increas- 
ing in  size,  and  we  may  imagine  him  speculating  as 
to  their  method  of  origin  and  thereasons  why  they 
adopt  this  or  that  shape.  But  in  spite  of  his  most 
acute  observations  and  his  most  ingenious  specu- 
lation, he  could  never  understand  the  real  signifi- 
cance of  the  cities,  since  he  is  not  acquainted 
with  the  actual  living  unit.  Imagine  now,  if  you 
will,  that  this  supramundane  observer  invents 
a telescope  which  enables  him  to  perceive  more 
minute  objects  and  thus  discovers  human  beings. 
What  a complete  revolution  this  would  make  in 
his  knowledge  of  mundane  affairs!  We  can 
imagine  how  rapidly  discovery  would  follow  dis- 
covery; how  it  would  be  found  that  it  was  the 
human  beings  that  build  the  houses,  construct 
and  run  the  railroads,  and  control  the  growth 
of  the  cities  according  to  their  fancy ; and,  lastly, 


60  THE  STORY  OF  THE  LIVING  MACHINE. 

how  it  would  be  learned  that  it  is  the  human  being 
alone  that  grows  and  multiplies  and  that  all  else 
is  the  result  of  his  activities.  Such  a supramun- 
dane  observer  would  find  himself  entering  into  a 
new  era,  in  which  all  his  previous  knowledge  would 
sink  into  oblivion. 

Something  of  this  same  sort  of  revolution  was 
inaugurated  in  the  study  of  living  things  by  the 
discovery  of  cells  and  protoplasms.  Animals  and 
plants  had  been  studied  for  centuries  and  many 
accurate  and  painstaking  observations  had  been 
made  upon  them.  Monumental  masses  of  evi- 
dence had  been  collected  bearing  upon  their 
shapes,  sizes,  distribution,  and  relations.  Anato- 
my had  long  occupied  the  attention  of  naturalists, 
and  the  general  structure  of  animals  and  plants 
was  already  well  known.  But  the  discoveries 
starting  in  the  fourth  decade  of  the  century  by 
disclosing  the  unity  of  activity  changed  the  aspect 
of  biological  science. 

The  Cell  Doctrine. — The  cell  doctrine  is,  in 
brief,  the  theory  that  the  bodies  of  animals  and 
plants  are  built  up  entirely  of  minute  elementary 
units,  more  or  less  independent  of  each  other,  and 
all  capable  of  growth  and  multiplication.  This 
doctrine  is  commonly  regarded  as  being  inau- 
gurated in  1839  by  Schwann.  Long  before  this, 
however,  many  microscopists  had  seen  that  the 
bodies  of  plants  are  made  up  of  elementary  units. 
In  describing  the  bark  of  a tree  in  1665,  Robert 
Hooke  had  stated  that  it  was  composed  of  little 
boxes  or  cells,  and  regarded  it  as  a sort  of  honey- 
comb structure  with  its  cells  filled  with  air.  The 
term  cell  quite  aptly  describes  the  compartments 
of  such  a structure,  as  can  be  seen  by  a glance  at 
pig.  7,  and  this  term  has  been  retained  even  till 


THE  CELL  AND  PROTOPLASM. 


6 1 


Fig.  7. — A bit  of  bark  show- 
ing cellular  structure. 


to-day  in  spite  of  the  fact  that  its  original  signifi- 
cance has  entirely  disappeared.  During  the  last 
century  not  a few  natural- 
ists observed  and  described 
these  little  vesicles,  always 
regarding  them  as  little 
spaces  and  never  looking 
upon  them  as  having  any 
significance  in  the  activities 
of  plants.  In  one  or  two 
instances  similar  bodies 
were  noticed  in  animals,  al- 
though no  connection  was 
drawn  between  them  and 
the  cells  of  plants.  In  the 
early  part  of  the  century  observations  upon  va- 
rious kinds  of  animals  and  plant  tissues  multi- 
plied, and  many  microscopists  independently  an- 
nounced the  discovery  of  similar  small  corpuscular 
bodies.  Finally,  in  1839,  these  observations  were 
combined  together  by  Schwann  into  one  general 
theory.  According  to  the  cell  doctrine  then  for- 
mulated, the  parts  of  all  animals  and  plants  are 
either  composed  of  cells  or  of  material  derived 
from  cells.  The  bark,  the  wood,  the  roots,  the 
leaves  of  plants  are  all  composed  of  little  vesicles 
similar  to  those  already  described  under  the  name 
of  cells.  In  animals  the  cellular  structure  is  not 
so  easy  to  make  out ; but  here  too  the  muscle,  the 
bone,  the  nerve,  the  gland  are  all  made  up  of  sim- 
ilar vesicles  or  of  material  made  from  them.  The 
cells  are  of  wonderfully  different  shapes  and  widely 
different  sizes,  but  in  general  structure  they  are 
alike.  These  cells,  thus  found  in  animals  and 
plants  alike,  formed  the  first  connecting  link  be- 
tween animals  and  plants.  This  discovery  was 


6 2 THE  STORY  OF  THE  LIVING  MACHINE. 

like  that  of  our  supposed  supramundane  observer 
when  he  first  found  the  human  being  that  brought 
into  connection  the  widely  different  cities  in  the 
various  parts  of  the  world. 

Schwann  and  his  immediate  followers,  while 
recognizing  that  the  bodies  of  animals  and  plants 
were  composed  of  cells,  were  at  a loss  to  explain 
how  these  cells  arose.  The  belief  held  at  first 
was  that  there  existed  in  the  bodies  of  animals 
and  plants  a structureless  substance  which  formed 
the  basis  out  of  which  the  cells  develop,  in  some- 
what the  same  way  that  crystals  arise  from  a 
mother  liquid.  This  supposed  substance  Schwann 
called  the  cytoblastema , and  he  thought  it  existed 
between  the  cells  or  sometimes  within  them.  For 
example,  the  fluid  part  of  the  blood  is  the  cyto- 
blastema, the  blood  corpuscles  being  the  cells. 
From  this  structureless  fluid  the  cells  were  sup- 
posed to  arise  by  a process  akin  to  crystallization. 
To  be  sure,  the  cells  grow  in  a manner  very  differ- 
ent from  that  of  a crystal.  A crystal  always  grows 
by  layers  being  added  upon  its  outside,  while  the 
cells  grow  by  additions  within  its  body.  But 
this  was  a minor  detail,  the  essential  point  being 
that  from  a structureless  liquid  containing  proper 
materials  the  organized  cell  separated  itself. 

This  idea  of  the  cytoblastema  was  early  thrown 
into  suspicion,  and  almost  at  the  time  of  the  an- 
nouncement of  the  cell  doctrine  certain  micro- 
scopists  made  the  claim  that  these  cells  did  not 
come  from  any  structureless  medium,  but  by  divi- 
sion from  other  cells  like  themselves.  This  claim, 
and  its  demonstration,  was  of  even  greater  im- 
portance than  the  discovery  of  the  cells.  For 
a number  of  years,  however,  the  matter  was  in 
dispute,  evidence  being  collected  which  about 


THE  CELL  AND  PROTOPLASM. 


63 


equally  attested  each  view.  It  was  a Scotchman, 
Dr.  Barry,  who  finally  produced  evidence  which 
settled  the  question  from  the  study  of  the  devel- 
oping egg. 

The  essence  of  his  discovery  was  as  follows: 
The  ovum  of  an  animal  is  a single  cell,  and  when 
it  begins  to  develop  into  an  embryo  it  first  simply 
divides  into  two  halves,  producing  two  cells  (Fig. 
8,  a and  b).  Each  of  these  in  turn  divides,  giving 
four,  and  by  repeated  divisions  of  this  kind  there 
arises  a solid  mass  of  smaller  cells  (Fig.  8,  b to  /,) 


Fig.  8.  —Successive  stages  in  the  division  of  the  developing  egg. 


called  the  mulberry  stage,  from  its  resemblance  to 
a berry.  This  is,  of  course,  simply  a mass  of  cells, 
each  derived  by  division  from  the  original.  As  the 
cells  increase  in  number,  the  mass  also  increases 
in  size  by  the  absorption  of  nutriment,  and  the 
cells  continue  dividing  until  the  mass  contains 
thousands  of  cells.  Meantime  the  body  of  the 
animal  is  formed  out  of  these  cells,  and  when  it  is 
adult  it  consists  of  millions  of  cells,  all  of  which 
have  been  derived  by  division  from  the  original 


64  THE  story  of  the  living  machine. 

cell.  In  such  a history  each  cell  comes  from  pre- 
existing  cells  and  a cytoblastema  plays  no  part. 

It  was  impossible,  however,  for  Barry  or  any 
other  person  to  follow  the  successive  divisions  of 
the  egg  cell  through  all  the  stages  to  the  adult. 
The  divisions  can  be  followed  for  a short  time 
under  the  microscope,  but  the  rest  must  be  a mat- 
ter of  simple  inference.  It  was  argued  that  since 
cell  origin  begins  in  this  way  by  simple  division, 
and  since  the  same  process  can  be  observed  in 
the  adult,  it  is  reasonable  to  assume  that  the  same 
process  has  continued  uninterruptedly,  and  that 
this  is  the  only  method  of  cell  origin.  But  a final 
demonstration  of  this  conclusion  was  not  forth- 
coming for  a long  time.  For  many  years  some 
biologists  continued  to  believe  that  cells  can  have 
other  origin  than  from  pre-existing  cells.  Year 
by  year  has  the  evidence  for  such  “ free  cell  ” 
origin  become  less,  until  the  view  has  been  en- 
tirely abandoned,  and  to-day  it  is  everywhere 
admitted  that  new  cells  always  arise  from  old 
ones  by  direct  descent,  and  thus  every  cell  in  the 
body  of  an  animal  or  plant  is  a direct  descendant 
by  division  from  the  original  egg  cell. 

The  Cell. — But  what  is  this  cell  which  forms 
the  unit  of  life,  and  to  which  all  the  fundamental 
vital  properties  can  be  traced  ? We  will  first 
glance  at  the  structure  of  the  cell  as  it  was  under- 
stood by  the  earlier  microscopists.  A typical  cell 
is  shown  in  Fig.  9.  It  will  be  seen  that  it  consists 
of  three  quite  distinct  parts.  There  is  first  the 
cell  wall  (w)  which  is  a limiting  membrane  of 
varying  thickness  and  shape.  This  is  in  reality 
lifeless  material,  and  is  secreted  by  the  rest  of  the 
cell.  Being  thus  produced  by  the  other  active 
parts  of  the  cell,  we  will  speak  of  it  as  formed 


THE  CELL  AND  PROTOPLASM. 


65 


material  in  distinction  from  the  rest,  which  is 
active  material.  Inside  this  vesicle  is  contained  a 
somewhat  transparent  semifluid  material  which 
has  received  various  names,  but  which  for  the 
present  we  will  call  cell  substance  (Fig.  9,  pr).  It 
may  be  abundant  or  scanty,  and  has  a widely 
varying  consistency  from  a very  liquid  mass  to  a 
decidedly  thick  jellylike  substance.  Lying  within 
the  cell  substance  is  a small  body,  usually  more 
or  less  spherical  in  shape,  which  is  called  the 
nucleus  (Fig.  9,  n).  It  appears  to  the  microscope 
similar  to  the  cell  sub- 
stance in  character, 
and  has  frequently 
been  described  as  a bit 
of  the  cell  substance 
more  dense  than  the 
remainder.  Lying 
within  the  nucleus 
there  are  usually  to 
be  seen  one  or  more 
smaller  rounded  bod- 
ies which  have  been 
called  nucleoli . From 

the  very  earliest  period  that  cells  have  been 
studied,  these  three  parts,  cell  wall,  cell  sub- 
stance, and  nucleus  have  been  recognized,  but 
as  to  their  relations  to  each  other  and  to  the 
general  activities  of  the  cell  there  has  been  the 
widest  variety  of  opinion. 

Cellular  Structure  of  Organisms. — It  will  be  well 
to  notice  next  just  what  is  meant  by  saying  that 
all  living  bodies  are  composed  of  cells.  This  can 
best  be  understood  by  referring  to  the  accompany- 
ing figures.  Figs.  10-14,  f°r  instance,  show  the 
microscopic  appearance  of  several  plant  tissues. 


Fig.  9. — A cell;  cw  is  the  cell  wall; 
pr,  the  cell  substance ; n,  the 
nucleus. 


66  THE  STORY  OF  THE  LIVING  MACHINE. 


At  Fig.  io  will  be  seen  the  tip  of  a root,  plainly 
made  of  cells  quite  similar  to  the  typical  cell  de- 
scribed. At  Fig.  ii  will  be  seen  a bit  of  a leaf 


Fig.  io. — Cells  at  a root  tip. 


showing  the  same  general  structure.  At  Fig.  12  is 
a bit  of  plant  tissue  of  which  the  cell  walls 
are  very  thick,  so  that  a very  dense  structure  is 

formed.  At  Fig.  13 
is  a bit  of  a potato 
showing  its  cells 
filled  with  small 
granules  of  starch 
which  the  cells 
have  produced  by 
their  activities  and 
deposited  within 
their  own  bodies. 
At  Fig.  14  are  sev- 
eral wood  cells 
showing  cell  walls 
of  different  shape 
which,  having  be- 
Fig.  ii. — Section  of  a leaf  showing  come  dead,  have 
cells  of  different  shapes.  lost  their  Contents 

and  simply  remain 
as  dead  cell  walls.  Each  was  in  its  earlier 
history  filled  with  cell  substance  and  contained 
a nucleus.  In  a similar  way  any  bit  of  vegetable 


THE  CELL  AND  PROTOPLASM.  67 

tissue  would  readily  show  itself  to  be  made  of 
similar  cells. 

In  animal  tissues  the  cellular  structure  is  not 
so  easily  seen,  largely  because  the  products  made 
by  the  cells,  the  formed  products,  become  relatively 

more  abundant 
and  the  cells 
themselves  not 
so  prominent. 
But  the  cellular 
structureisnone 
the  less  demon- 
Fig.  12. — Plant  cells  with  thick  walls,  from  gtrable  In  Tip* 
a fern.  c 

15,  for  instance, 

will  be  seen  a bit  of  cartilage  where  the  cells  them- 
selves are  rather  small,  while  the  material  depos- 
ited between  them  is  abundant.  This  material 
between  the  cells  is  really  to  be  regarded  as 
an  excessively  thickened  cell  wall  and  has  been 
secreted  by 
the  cell  sub- 
stance lying 
within  the 
cells,  so  that 
a bit  of  car- 
tilage is  really 
a mass  of  cells 
with  an  excep- 
tionally thick 
cell  wall.  At 

jTjp.  j ^ Fig.  13. — Section  of  a potato  showing  different 

, ..  * shaped  cells,  the  inner  and  larger  ones  being 

Shown  a little  filled  with  grains  of  starch, 

blood.  Here 

the  cells  are  to  be  seen  floating  in  a liquid.  The 
liquid  is  colourless  and  it  is  the  red  colour  in 
the  blood  cells  which  gives  the  blood  its  red 


68  THE  STORY  OF  THE  LIVING  MACHINE. 


colour.  The  liquid  may  here  again  be  regarded 
as  material  produced  by  cells.  At  Fig.  17  is  a 

bit  of  bone  showing 
small  irregular  cells 
imbedded  within  a 
large  mass  of  mate- 
rial which  has  been 
deposited  by  the  cell. 
In  this  case  the 
formed  material  has 
been  hardened  by 
'calcium  phosphate, 
which  gives  the  rigid 
consistency  to  the 
bone.  In  some  ani- 
mal tissues  the 
formed  material  is 
still  greater  in 
amount.  At  Fig.  18, 
for  example,  is  a bit 
of  connective  tissue,  made  up  of  a mass  of  fine 
fibres  which  have  no  resemblance  to  cells,  and  in- 
deed arenot  cells.  These  fibres  have,  however, been 
made  by  cells,  and  a careful 
study  of  such  tissue  at  proper 
places  will  show  the  cells  with- 
in it.  The  cells  shown  in 
Fig.  18  (r)  have  secreted  the 
fibrous  material.  Fig.  19 
shows  a cell  composing  a bit 
of  nerve.  At  Fig.  20  is  a bit 
of  muscle;  the  only  trace  of 
cellular  structure  that  it 
shows  is  in  the  nuclei  (//),  but 
if  the  muscle  be  studied  in  a 
young  condition  its  cellular 


Fig.  14.— Various  shaped  wood  cells 
from  plant  tissue. 


Fig.  15.— A*  bit  of  cartilage. 


THE  CELL  AND  PROTOPLASM.  69 

structure  is  more  evident.  Thus  it  happens  in 
adult  animals  that  the  cells  which  are  large  and 
clear  at  first,  become  less  and  less  evident,  until 
the  adult  tissue 
seems  sometimes  to 
be  composed  most- 
ly of  what  we  have 
called  formed  ma- 
terial. 

It  must  not  be 
imagined,  however, 
that  a very  rigid 
line  can  be  drawn 
between  the  cell 
itself  and  the  ma- 
terial it  forms. 

The  formed  material  is  in  many  cases  simply  a 
thickened  cell  wall,  and  this  we  commonly  regard 
as  part  of  the  cell.  In  many  cases  the  formed 
material  is  simply  the  old 
dead  cell  walls  from  which 
the  living  substance  has 
been  withdrawn  (Fig.  14). 
In  other  cases  the  cell 
substance  acquires  peculiar 
functions,  so  that  what 
seems  to  be  the  formed 
material  is  really  a modified 
cell  body  and  is  still  active 
and  alive.  Such  is  the  case 
in  the  muscle.  In  other 
FlG-  17.—  A bit  of  bone  cases  the  formed  material 
in  the  bony  matter.  appears  to  be  manufactured 

within  the  cell  and  secret- 
ed, as  in  the  case  of  bone.  No  sharp  lines  can  be 
drawn,  however,  between  the  various  types.  But 


Fig.  16. — Frog’s  blood  : a and  b are  the 
cells;  c is  the  liquid. 


70  THE  STORY  OF  THE  LIVING  MACHINE. 


the  distinction 
cell  body  is  a 


between  formed  material  and 
convenient  one  and  may  well 
be  retained  in  the  discussion 
of  cells.  In  our  discussion  of 
the  fundamental  vital  proper- 
ties we  are  only  concerned  in 
the  cell  substance,  the  formed 
material  having  nothing  to  do 
with  fundamental  activities  of 
life,  although  it  forms  largely 
the  secondary  ma- 
chinery which  we 
have  already  studied. 

In  all  higher  an- 
imals and  plants  the 
life  of  the  individual 
begins  as  a single 
ovum  or  a single 
cell,  and  as  it  grows 
the  cells  increase 
rapidly  until  the  adult  is  formed  out  of 
hundreds  of  millions  of  cells.  As  these 
cells  become  numerous  they  cease,  after 
a little,  to  be  alike.  They  assume  differ- 
ent shapes  which  are  adapted  to  the 
different  duties  they  are  to  perform. 

Thus,  those  cells  which  are  to  form  bone 
soon  become  different  from  those  which 
are  to  form  muscle,  and  those  which  are 
to  form  the  blood  are  quite  unlike  those 
which  are  to  produce  the  hairs.  By 
means  of  such  a differentiation  there 
arises  a very  complex  mass  of  cells, 
with  great  variety  in  shape  and  function. 

It  should  be  noticed  further  that 
some  animals  and  plants  in  which 


Fig.  18. — Connective 
tissue.  The  cells 
of  the  tissue  are 
shown  at  c,  and  the 
fibres  or  formed 
matter  at  f. 


Fig.  19. 

A piece  of 
nerve  fibre, 
showing  the 
cell  with  its 
nucleus  at  n. 

there  are 
the  whole 


THE  CELL  AND  PROTOPLASM. 


71 


Fig.  20. — A muscle  fibre. 
The  nucleii  are  shown 
at  n. 


animal  is  composed  of  a single  cell.  These 
organisms  are  usually  of  extremely  minute  size, 
and  they  comprise  most  of 
the  so-called  animalculae 
which  are  found  in  water. 

In  such  animals  the  differ- 
ent parts  of  the  cell  are  mod- 
ified to  perform  different 
functions.  The  different  or- 
gans appear  within  the  cell, 
and  the  cell  is  more  complex 
than  the  typical  cell  described. 

Fig.  21  shows  such  a cell. 

Such  an  animal  possesses 
several  organs,  but,  since  it 
consists  of  a single  mass  of 
protoplasm  and  a single  nu- 
cleus, it  is  still  only  a single 
cell.  In  the  multicellular  or- 
ganisms the  organs  of 
the  body  are  made  up  of 
cells,  and  the  different 
organs  are  produced 
by  a differentiation  of 
cells,  but  in  the  uni- 
cellular organisms  the 
organs  are  the  results 
of  the  differentiation  of 
the  parts  of  a single 
cell.  In  the  one  case 
there  is  a differentiation 
of  cells,  and  in  the 
other  of  the  parts  of  a 

Fig.  21. — A complex  cell.  It  is  Ce^i*  , . , . f , 

t an  entire  animal,  but  composed  oUCn,  in  Driet,  IS  the 
of  only  one  cell.  cell  to  whose  activities 

6 


72  THE  STORY  OF  THE  LIVING  MACHINE. 

it  is  possible  to  trace  the  fundamental  properties  of 
all  living  things.  Cells  are  endowed  with  the  prop- 
erties of  irritability,  contractibility,  assimilation 
and  reproduction,  and  it  is  thus  plainly  to  the 
study  of  cells  that  we  must  look  for  an  interpreta- 
tion of  life  phenomena.  If  we  can  reach  an  intel- 
ligible understanding  of  the  activities  of  the  cell 
our  problem  is  solved,  for  the  activities  of  the 
fully  formed  animal  or  plant,  however  complex, 
are  simply  the  application  of  mechanical  and  chem- 
ical principles  among  the  groups  of  such  cells. 
But  wherein  does  this  knowledge  of  cells  help  us? 
Are  we  any  nearer  to  understanding  how  these 
vital  processes  arise  ? In  answer  to  this  question 
we  may  first  ask  whether  it  is  possible  to  determine 
whether  any  one  part  of  the  cell  is  the  seat  of  its 
activities. 

The  Cell  Wall.— T he  first  suggestion  which 
arose  was  that  the  cell  wall  was  the  important 
part  of  the  cell,  the  others  being  secondary.  This 
was  not  an  unnatural  conclusion.  The  cell  wall 
is  the  most  persistent  part  of  the  cell.  It  was  the 
part  first  discovered  by  the  microscope  and  is  the 
part  which  remains  after  the  other  parts  are  gone. 
Indeed,  in  many  of  the  so-called  cells  the  cell  wall 
is  all  that  is  seen,  the  cell  contents  having  disap- 
peared (Fig.  14).  It  was  not  strange,  then,  that 
this  should  at  first  have  been  looked  upon  as  the 
primary  part.  The  idea  was  that  the  cell  wall  in 
some  way  changed  the  chemical  character  of  the 
substances  in  contact  with  its  two  sides,  and  thus 
gave  rise  to  vital  activities  which,  as  we  have 
seen,  are  fundamentally  chemical.  Thus  the  cell 
wall  was  regarded  as  the  most  essential  part  of 
the  cell,  since  it  controlled  its  activities.  This 
was  the  belief  of  Schwann,  although  he  also  re- 


THE  CELL  AND  PROTOPLASM. 


73 


garded  the  other  parts  of  the  cell  as  of  import- 
ance. 

This  conception,  however,  was  quite  tempo- 
rary. It  was  much  as  if  our  hypothetical  supra- 
mundane  observer  looked  upon  the  clothes  of 
his  newly  discovered  human  being  as  forming  the 
essential  part  of  his  nature.  It  was  soon  evident 
that  this  position  could  not 
be  maintained.  It  was 
found  that  many  bits  of 
living  matter  were  entirely 
destitute  of  cell  wall.  This 
is  especially  true  of  animal 
cells.  While  among  plants 
the  cell  wall  is  almost  al- 
ways well  developed,  it  is 
very  common  for  animal 
cells  to  be  entirely  lacking 
in  this  external  covering — 
as,  for  example,  the  white 
blood-cells.  Fig.  22  shows  an 
amoeba,  a cell  with  very  ac- 
tive  powers  of  motion  and 
assimilation,  but  with  no  " 
cell  wall.  Moreover,  young 
cells  are  always moreactive 
than  older  ones,  and  they 
commonly  possess  either 
no  cell  wall  or  a very  slight 
one,  this  being  deposited 
as  the  cell  becomes  older  and  remaining  long 
after  it  is  dead.  Such  facts  soon  disproved  the 
notion  that  the  cell  wall  is  a vital  part  of  the  cell, 
and  a new  conception  took  its  place  which  was  to 
have  a more  profound  influence  upon  the  study 
of  living  things  than  any  discovery  hitherto 


Fig.  22. — An  amoeba.  A sin- 
gle cell  without  cell  wall. 
n is  the  nucleus ; f,  a bit 
of  food  which  the  cell  has 
absorbed. 


74  THE  story  of  the  living  machine. 

made.  This  was  the  formulation  of  the  doctrine 
of  the  nature  of  protoplasm. 

Protoplasm. — (a)  Discovery.  As  it  became  evi- 
dent that  the  cell  wall  is  a somewhat  inactive 
part  of  the  cell,  more  attention  was  put  on  the 
cell  contents.  For  twenty  years  after  the  formu- 
lation of  the  cell  doctrine  both  the  cell  substance 
and  the  nucleus  had  been  looked  upon  as  essen- 
tial to  its  activities.  This  was  more  especially 
true  of  the  nucleus,  which  had  been  thought  of  as 
an  organ  of  reproduction.  These  suggestions  ap- 
peared indefinitely  in  the  writings  of  one  scien- 
tist and  another,  and  were  finally  formulated  in 
i860  into  a general  theory  which  formed  what  has 
sometimes  been  called  the  starting  point  of  mod- 
ern biology.  From  that  time  the  material  known 
as  protoplasm  was  elevated  into  a prominent  po- 
sition in  the  discussion  of  all  subjects  connected 
with  living  phenomena.  The  idea  of  protoplasm 
was  first  clearly  defined  by  Schultze,  who  claimed 
that  the  real  active  part  of  the  cell  was  the  cell 
substance  within  the  gell  wall.  This  substance 
he  proved  to  be  endowed  with  powers  of  motion 
and  powers  of  inducing  chemical  changes  asso- 
ciated with  vital  phenomena.  He  showed  it  to 
be  the  most  abundant  in  the  most  active  cells, 
becoming  less  abundant  as  the  cells  lose  their  ac- 
tivity, and  disappearing  when  the  cells  lose  their 
vitality.  This  cell  substance  was  soon  raised  into 
a position  of  such  importance  that  the  smaller 
body  within  it  was  obscured,  and  for  some  twenty 
years  more  the  nucleus  was  silently  ignored  in 
biological  discussion.  According  to  Schultze,  the 
cell  substance  itself  constituted  the  cell,  the  other 
parts  being  entirely  subordinate,  and  indeed  fre- 
quently absent.  A cell  was  thus  a bit  of  proto- 


THE  CELL  AND  PROTOPLASM.  75 

plasm,  and  nothing  more.  But  the  more  impor- 
tant feature  of  this  doctrine  was  not  the  simple 
conclusion  that  the  cell  substance  constitutes  the 
cell,  but  the  more  sweeping  conclusion  that  this 
cell  substance  is  in  all  cells  essentially  identical. 
The  study  of  all  animals,  high  and  low,  showed 
all  active  cells  filled  with  a similar  material,  and 
more  important  still,  the  study  of  plant  cells  dis- 
closed a material  strikingly  similar.  Schultze  ex- 
perimented with  this  material  by  all  means  at  his 
command,  and  finding  that  the  cell  substance  in 
all  animals  and  plants  obeys  the  same  tests, 
reached  the  conclusion  that  the  cell  substance  in 
animals  and  plants  is  always  identical.  To  this 
material  he  now  gave  the  name  protoplasm,  choos- 
ing a name  hitherto  given  to  the  cell  contents  of 
plant  cells.  From  this  time  forth  this  term  proto- 
plasm was  applied  to  the  living  material  found  in 
all  cells,  and  became  at  once  the  most  important 
factor  in  the  discussion  of  biological  problems. 

The  importance  of  this  newly  formulated  doc- 
trine it  is  difficult  to  appreciate.  Here,  in  proto- 
plasm had  been  apparently  found  the  foundation 
of  living  phenomena.  Here  was  a substance  uni- 
versally present  in  animals  and  plants,  simple  and 
uniform — a substance  always  present  in  living 
parts  and  disappearing  with  death.  It  was  the 
simplest  thing  that  had  life,  and  indeed  the  only 
thing  that  had  life,  for  there  is  no  life  outside  of 
cells  and  protoplasm.  But  simple  as  it  was  it  had 
all  the  fundamental  properties  of  living  things — 
irritability,  contractibility,  assimilation,  and  repro- 
duction. It  was  a compound  which  seemingly 
deserved  the  name  of  “ physical  basis  of  life,”  which 
was  soon  given  to  it  by  Huxley.  With  this  con- 
ception of  protoplasm  as  the  physical  basis  of  life 


76  THE  STORY  OF  THE  LIVING  MACHINE. 


the  problems  connected  with  the  study  of  life  be- 
came more  simplified.  In  order  to  study  the  na- 
ture of  life  it  was  no  longer  necessary  to  study 
the  confusing  mass  of  complex  organs  disclosed 
to  us  by  animals  and  plants,  or  even  the  some- 
what less  confusing  structures  shown  by  individ- 
ual cells.  Even  the  simple  cell  has  several  sep- 
arate parts  capable  of  undergoing  great  modifica- 
tions in  different  types  of  animals.  This  confusion 
now  appeared  to  vanish,  for  only  one  thing  was 
found  to  be  alive,  and  that  was  apparently  very 
simple.  But  that  substance  exhibited  all  the  prop- 
erties of  life.  It  moved,  it  could  grow,  and  re- 
produce itself,  so  that  it  was  necessary  only  to 
explain  this  substance  and  life  would  be  explained. 

(b)  Nature  of  Protoplasm. — What  is  this  ma- 
terial, protoplasm  ? As  disclosed  by  the  early 
microscope  it  appeared  to  be  nothing  more 
than  a simple  mass  of  jelly,  usually  transparent, 
more  or  less  consistent,  sometimes  being  quite 
fluid,  and  at  others  more  solid.  Structure  it  ap- 
peared to  have  none.  Its  chief  peculiarity,  so 
far  as  physical  characters  were  concerned,  was 
a wonderful  and  never-ceasing  activity.  This 
jellylike  material  appeared  to  be  endowed  with 
wonderful  powers,  and  yet  neither  physical  nor 
microscopical  study  revealed  at  first  anything 
more  than  a uniform  homogeneous  mass  of  jelly. 
Chemical  study  of  the  same  substance  was  of 
no  less  interest  than  the  microscopical  study. 
Of  course  it  was  no  easy  matter  to  collect  this 
protoplasm  in  sufficient  quantity  and  pure  enough 
to  make  a careful  analysis.  The  difficulties  were 
in  time,  however,  overcome,  and  chemical  study 
showed  protoplasm  to  be  a proteid,  related  to 
other  proteids  like  albumen,  but  one  which  was 


THE  CELL  AND  PROTOPLASM.  77 

more  complex  than  any  other  known.  It  was  for 
a long  time  looked  upon  by  many  as  a single 
definite  chemical  compound,  and  attempts  were 
made  to  determine  its  chemical  formula.  Such 
an  analysis  indicated  a molecule  made  up  of  sev- 
eral hundred  atoms.  Chemists  did  not,  however, 
look  with  much  confidence  upon  these  results, 
and  it  is  not  surprising  that  there  was  no  very  close 
agreement  among  them  as  to  the  number  of  atoms 
in  this  supposed  complex  molecule.  Moreover, 
from  the  very  first,  some  biologists  thought  pro- 
toplasm to  be  not  one,  but  more  likely  a mixture 
of  several  substances.  But  although  it  was  more 
complex  than  any  other  substance  studied,  its 
general  characters  were  so  like  those  of  albumen 
that  it  was  uniformly  regarded  as  a proteid;  but 
one  which  was  of  a higher  complexity  than  others, 
forming  perhaps  the  highest  number  of  a series 
of  complex  chemical  compounds,  of  which  ordinary 
proteids,  such  as  albumen,  formed  lower  mem- 
bers. Thus,  within  a few  years  following  the  dis- 
covery of  protoplasm  there  had  developed  a theory 
that  living  phenomena  are  due  to  the  activities  of 
a definite  though  complex  chemical  compound, 
composed  chiefly  of  the  elements  carbon,  oxygen, 
hydrogen,  and  nitrogen,  and  closely  related  to 
ordinary  proteids.  This  substance  was  the  basis 
of  living  activity,  and  to  its  modification  under 
different  conditions  were  due  the  miscellaneous 
phenomena  of  life. 

(c)  Significance  of  Protoplasm. — The  philosophi- 
cal significance  of  this  conception  was  very  far- 
reaching.  The  problem  of  life  was  was  so  simpli- 
fied by  substituting  the  simple  protoplasm  for  the 
complex  organism  that  its  solution  seemed  to  be 
not  very  difficult.  This  idea  of  a chemical  com- 


78  THE  STORY  OF  THE  LIVING  MACHINE. 

pound  as  the  basis  of  all  living  phenomena  gave 
rise  in  a short  time  to  a chemical  theory  of  life 
which  was  at  least  tenable,  and  which  accounted 
for  the  fundamental  properties  of  life.  That 
theory,  the  chemical  theory  of  life,  may  be  outlined 
somewhat  as  follows: 

The  study  of  the  chemical  nature  of  sub- 
stances derived  from  living  organisms  has  devel- 
oped into  what  has  been  called  organic  chemis- 
try. Organic  chemistry  has  shown  that  it  is  pos- 
sible to  manufacture  artificially  many  of  the  com- 
pounds which  are  called  organic,  and  which  had 
been  hitherto  regarded  as  produced  only  by  living 
organisms.  At  the  beginning  of  the  century,  it 
was  supposed  to  be  impossible  to  manufacture  by 
artificial  means  any  of  the  compounds  which  ani- 
mals and  plants  produce  as  the  result  of  their  life. 
But  chemists  were  not  long  in  showing  that  this 
position  is  untenable.  Many  of  the  organic  prod- 
ucts were  soon  shown  capable  of  production  by  ar- 
tificial means  in  the  chemist’s  laboratory.  These 
organic  compounds  form  a series  beginning  with 
such  simple  bodies  as  carbonic  acid  (C02),  water 
(H20),and  ammonia  (NH3),and  passing  up  through 
a large  number  of  members  of  greater  and  greater 
complexity,  all  composed,  however,  chiefly  of  the 
elements  carbon,  oxygen,  hydrogen,  and  nitrogen. 
Our  chemists  found  that  starting  with  simple  sub- 
stances they  could,  by  proper  means,  combine 
them  into  molecules  of  greater  complexity,  and  in 
so  doing  could  make  many  of  the  compounds 
that  had  hitherto  been  produced  only  as  a result 
of  living  activities.  For  example,  urea,  formic 
acid,  indigo,  and  many  other  bodies,  hitherto  pro- 
duced only  by  animals  and  plants,  were  easily 
produced  by  the  chemist  by  purely  chemical  meth- 


THE  CELL  AND  PROTOPLASM.  . 79 

ods.  Now  when  protoplasm  had  been  discovered 
as  the  “ physical  basis  of  life,”  and,  when  it  was 
further  conceived  that  this  substance  is  a pro- 
teid  related  to  albumens,  it  was  inevitable  that  a 
theory  should  arise  which  found  the  explanation 
of  life  in  accordance  with  simple  chemical  laws. 

If,  as  chemists  and  biologists  then  believe, 
protoplasm  is  a compound  which  stands  at  the 
head  of  the  organic  series,  and  if,  as  is  the  fact, 
chemists  are  each  year  succeeding  in  making 
higher  and  higher  members  of  the  series,  it  is  an 
easy  assumption  that  some  day  they  will  be  able 
to  make  the  highest  member  of  the  series.  Fur- 
ther, it  is  a well-known  fact  that  simple  chemical 
compounds  have  simple  physical  properties,  while 
the  higher  ones  have  more  varied  properties. 
Water  has  the  property  of  being  liquid  at  certain 
temperatures  and  solid  at  others,  and  of  dividing 
into  small  particles  (i.  e.,  dissolving)  certain  bodies 
brought  in  contact  with  it.  The  higher  com- 
pound albumen  has,  however,  a great  number  of 
properties  and  possibilities  of  combination  far  be- 
yond those  of  water.  Now  if  the  properties  in- 
crease in  complexity  with  the  complexity  of  the 
compound,  it  is  again  an  easy  assumption  that 
when  we  reach  a compound  as  complex  as  pro- 
toplasm, it  will  have  properties  as  complex  as 
those  of  the  simple  life  substance.  Nor  was  this 
such  a very  wild  hypothesis.  After  all,  the  fun- 
damental life  activities  may  all  be  traced  to  the 
simple  oxidation  of  food,  for  this  results  in  move- 
ment, assimilation,  and  growth,  and  the  result  of 
growth  is  reproduction.  It  was  therefore  only 
necessary  for  our  biological  chemists  to  suppose 
that  their  chemical  compound  protoplasm  pos- 
sessed the  power  of  causing  certain  kinds  of  oxi- 


So  THE  STORY  OF  THE  LIVING  MACHINE. 

dation  to  take  place,  just  as  water  itself  induces 
a simpler  kind  of  oxidation,  and  they  would  have 
a mechanical  explanation  of  the  life  activities. 
It  was  certainly  not  a very  absurd  assumption 
to  make,  that  this  substance  protoplasm  could 
have  this  power,  and  from  this  the  other  vital  ac- 
tivities are  easily  derived. 

In  other  words,  the  formulation  of  the  doctrine 
of  protoplasm  made  it  possible  to  assume  that 
life  is  not  a distinct  force,  but  simply  a name 
given  to  the  properties  possessed  by  that  highly 
complex  chemical  compound  protoplasm.  Just 
as  we  might  give  the  name  aquacity  to  the  prop- 
erties possessed  by  water,  so  we  have  actually 
given  the  name  vitality  to  the  properties  possessed 
by  protoplasm.  To  be  sure,  vitality  is  more  mar- 
velous than  aquacity,  but  so  is  protoplasm  a more 
complex  compound  than  water.  This  compound 
was  a very  unstable  compound,  just  as  is  a mass 
of  gunpowder,  and  hence  it  is  highly  irritable,  also 
like  gunpowder,  and  any  disturbance  of  its  condi- 
tion produces  motion,  just  as  a spark  will  do  in  a 
mass  of  gunpowder.  It  is  capable  of  inducing 
oxidation  in  foods,  something  as  water  induces 
oxidation  in  a bit  of  iron.  The  oxidation  is,  how- 
ever, of  a different  kind,  and  results  in  the  forma- 
tion of  different  chemical  combinations;  but  it  is 
the  basis  of  assimilation.  Since  now  assimilation 
is  the  foundation  of  growth  and  reproduction,  this 
mechanical  theory  of  life  thus  succeeded  in  tracing 
to  the  simple  properties  of  the  chemical  com- 
pound protoplasm,  all  the  fundamental  proper- 
erties  of  life.  Since  further,  as  we  have  seen  in 
our  first  chapter,  the  more  complex  properties  of 
higher  organisms  are  easily  deduced  from  these 
simple  ones  by  the  application  of  the  laws  of 


THE  CELL  AND  PROTOPLASM. 


8l 


mechanics,  we  have  here  in  this  mechanical  theory 
of  life  the  complete  reduction  of  the  body  to  a 
machine. 

The  Eeign  of  Protoplasm. — This  substance  pro- 
toplasm became  now  naturally  the  centre  of  bio- 
logical thought.  The  theory  of  protoplasm  arose 
at  about  the  same  time  that  the  doctrine  of 
evolution  began  to  be  seriously  discussed  under 
the  stimulus  of  Darwin,  and  naturally  these  two 
great  conceptions  developed  side  by  side.  Evolu- 
tion was  constantly  teaching  that  natural  forces 
are  sufficient  to  account  for  many  of  the  com- 
plex phenomena  which  had  hitherto  been  regard- 
ed as  insolvable  ; and  what  more  natural  than  the 
same  kind  of  thinking  should  be  applied  to  the 
vital  activities  manifested  by  this  substance  proto- 
plasm. While  the  study  of  plants  and  animals 
was  showing  scientists  that  natural  forces  would 
explain  the  origin  of  more  complex  types  from 
simpler  ones  through  the  law  of  natural  selection, 
here  in  this  conception  of  protoplasm  was  a theory 
which  promised  to  show  how  the  simplest  forms 
may  have  been  derived  from  the  non-living.  For 
an  explanation  of  the  origin  of  life  by  natural 
means  appeared  now  to  be  a simple  matter. 

It  required  now  no  violent  stretch  of  the  im- 
agination to  explain  the  origin  of  life  something 
as  follows  : We  know  that  the  chemical  elements 
have  certain  affinities  for  each  other,  and  will 
unite  with  each  other  under  proper  conditions. 
We  know  that  the  methods  of  union  and  the  re- 
sulting compounds  vary  with  the  conditions  under 
which  the  union  takes  place.  We  know  further 
that  the  elements  carbon,  hydrogen,  oxygen,  and 
nitrogen  have  most  remarkable  properties,  and 
unite  to  form  an  almost  endless  series  of  remark- 


8 2 THE  STORY  OF  THE  LIVING  MACHINE. 

able  bodies  when  brought  into  combination  under 
different  conditions.  We  know  that  by  varying 
the  conditions  the  chemist  can  force  these  ele- 
ments to  unite  into  a most  extraordinary  variety 
of  compounds  with  an  equal  variety  of  properties. 
What  more  natural,  then,  than  the  assumption 
that  under  certain  conditions  these  same  elements 
would  unite  in  such  a way  as  to  form  this  com- 
pound protoplasm  ; and  then,  if  the  ideas  con- 
cerning protoplasm  were  correct,  this  body  would 
show  the  properties  of  protoplasm,  and  therefore 
be  alive.  Certainly  such  a supposition,  was  not 
absurd,  and  viewed  in  the  light  of  the  rapid  ad- 
vance in  the  manufacture  of  organic  compounds 
could  hardly  be  called  improbable.  Chemists  be- 
ginning with  simple  bodies  like  C02  and  H20 
were  climbing  the  ladder,  each  round  of  which 
was  represented  by  compounds  of  higher  com- 
plexity. At  the  top  was  protoplasm,  and  each 
year  saw  our  chemists  nearer  the  top  of  the  ladder, 
and  thus  approaching  protoplasm  as  their  final 
goal.  They  now  began  to  predict  that  only  a few 
more  years  would  be  required  for  chemists  to  dis- 
cover the  proper  conditions,  and  thus  make  proto- 
plasm. As  late  as  1880  the  prediction  was  freely 
made  that  the  next  great  discovery  would  be  the 
manufacture  of  a bit  of  protoplasm  by  artificial 
means,  and  thus  in  the  artificial  production  of 
life.  The  rapid  advance  in  organic  chemistry 
rendered  this  prediction  each  year  more  and  more 
probable.  The  ability  of  chemists  to  manufacture 
chemical  compounds  appeared  to  be  unlimited, 
and  the  only  question  in  regard  to  their  ability 
to  make  protoplasm  thus  resolved  itself  into  the 
question  of  whether  protoplasm  is  really  a chemi- 
cal compound. 


THE  CELL  AND  PROTOPLASM.  83 

We  can  easily  understand  how  eager  biologists 
became  now  in  pursuit  of  the  goal  which  seemed 
almost  within  their  reach  ; how  interested  they 
were  in  any  new  discovery,  and  how  eagerly  they 
sought  for  lower  and  simpler  types  of  protoplasm 
since  these  would  be  a step  nearer  to  the  earliest 
undifferentiated  life  substance.  Indeed  so  eager 
was  this  pursuit  for  pure  undifferentiated  proto- 
plasm, that  it  led  to  one  of  those  unfounded  dis- 
coveries which  time  showed  to  be  purely  im- 
aginary. When  this  reign  of  protoplasm  was  at 
its  height  and  biologists  were  seeking  for  even 
greater  simplicity  a most  astounding  discovery 
was  announced.  The  British  exploring  ship 
Challenger  had  returned  from  its  voyage  of  dis- 
covery and  collection,  and  its  various  treasures 
were  turned  over  to  the  different  scientists  for 
study.  The  brilliant  Prof.  Huxley,  who  had  first 
formulated  the  mechanical  theory  of  life,  now 
startled  the  biological  world  with  the  statement 
that  these  collections  had  shown  him  that  at 
the  bottom  of  the  deep  sea,  in  certain  parts 
of  the  world,  there  exists  a diffused  mass  of 
living  undifferentiated  protoplasm.  So  simple  and 
undifferentiated  was  it  that  it  was  not  divided 
into  cells  and  contained  no  nucleii.  It  was,  in 
short,  exactly  the  kind  of  primitive  protoplasm 
which  the  evolutionist  wanted  to  complete  his 
chain  of  living  structures,  and  the  biologist 
wanted  to  serve  as  a foundation  for  his  mechani- 
cal theory  of  life.  If  such  a diffused  mass  of  un- 
differentiated protoplasm  existed  at  the  bottom 
of  the  sea,  one  could  hardly  doubt  that  it  was 
developed  there  by  some  purely  natural  forces. 
The  discovery  was  a startling  one,  for  it  seemed 
that  the  actual  starting  point  of  life  had  been 


84  THE  story  of  the  living  machine. 

reached.  Huxley  named  his  substance  Bathybias , 
and  this  name  became  in  a short  time  familiar 
to  every  one  who  was  thinking  of  the  problems 
of  life.  But  the  discovery  was  suspected  from 
the  first,  because  it  was  too  closely  in  accord 
with  speculation,  and  it  was  soon  disproved.  Its 
discoverer  soon  after  courageously  announced 
to  the  world  that  he  had  been  entirely  mistaken, 
and  that  the  Bathybias,  so  far  from  being  un- 
differentiated protoplasm,  was  not  an  organic 
product  at  all,  but  simply  a mineral  deposit  in 
the  sea  water  made  by  purely  artificial  means. 
Bathybias  stands  therefore  as  an  instance  of  a too 
precipitate  advance  in  speculation,  which  led  even 
such  a brilliant  man  as  Prof.  Huxley  into  an  un- 
fortunate error  of  observation  ; for,  beyond  ques- 
tion, he  would  never  have  made  such  a mistake 
had  he  not  been  dominated  by  his  speculative 
theories  as  to  the  nature  of  protoplasm. 

But  although  Bathybias  proved  delusive,  this 
did  not  materially  affect  the  advance  and  develop- 
ment of  the  doctrine  of  protoplasm.  Simple  forms 
of  protoplasm  were  found,  although  none  quite  so 
simple  as  the  hypothetical  Bathybias.  The  univer- 
sal presence  of  protoplasm  in  the  living  parts  of 
all  animals  and  plants  and  its  manifest  activities 
completely  demonstrated  that  it  was  the  only  liv- 
ing substance,  and  as  the  result  of  a few  years  of 
experiment  and  thought  the  biologist’s  conception 
of  life  crystallized  into  something  like  this:  Liv- 
ing organisms  are  made  of  cells,  but  these  cells 
are  simply  minute  independent  bits  of  proto- 
plasm. They  may  contain  a nucleus  or  they  may 
not,  but  the  essence  of  the  cell  is  the  protoplasm, 
this  alone  having  the  fundamental  activities  of  life. 
These  bits  of  living  matter  aggregate  themselves 


THE  CELL  AND  PROTOPLASM.  85 

together  into  groups  to  form  colonies.  Such  colo- 
nies are  animals  or  plants.  The  cells  divide  the 
work  of  the  colony  among  themselves,  each  cell 
adopting  a form  best  adapted  for  the  special  work 
it  has  to  do.  The  animal  or  plant  is  thus  simply 
an  aggregate  of  cells,  and  its  activities  are  the 
sum  of  the  activities  of  its  separate  cells;  just  as 
the  activities  of  a city  are  the  sum  of  the  activities 
of  its  individual  inhabitants.  The  bit  of  proto- 
plasm was  the  unit,  and  this  was  a chemical  com- 
pound or  a simple  mixture  of  compounds  to  whose 
combined  physical  properties  we  have  given  the 
name  vitality. 

The  Decline  of  the  Reign  of  Protoplasm. — Hard- 
ly had  this  extreme  chemical  theory  of  life  been 
clearly  conceived  before  accumulating  facts  began 
to  show  that  it  is  untenable  and  that  it  must  at 
least  be  vastly  modified  before  it  can  be  received. 
The  foundation  of  the  chemical  theory  of  life 
was  the  conception  that  protoplasm  is  a definite 
though  complex  chemical  compound.  But  after  a 
few  years’  study  it  appeared  that  such  a concep- 
tion of  protoplasm  was  incorrect.  It  had  long 
been  suspected  that  protoplasm  was  more  complex 
than  was  at  first  thought.  It  was  not  even  at  the 
outset  found  to  be  perfectly  homogeneous,  but 
was  seen  to  contain  minute  granules,  together 
with  bodies  of  larger  size.  Although  these  bodies 
were  seen  they  were  regarded  as  accidental  or  sec- 
ondary, and  were  not  thought  of  as  forming  any 
serious  objection  to  the  conception  of  protoplasm 
as  a definite  chemical  compound.  But  modern 
opticians  improved  their  microscopes,  and  micro- 
scopists  greatly  improved  their  methods.  With 
the  new  microscopes  and  new  methods  there  be- 
gan to  appear,  about  twenty  years  ago,  new  reve- 


86  THE  STORY  OF  THE  LIVING  MACHINE. 

lations  in  regard  to  this  protoplasm.  Its  lack  of 
homogeneity  became  more  evident,  until  there  has 
finally  been  disclosed  to  us  the  significant  fact 
that  protoplasm  is  to  be  regarded  as  a substance 
not  only  of  chemical  but  also  of  high  mechanical 
complexity.  The  idea  of  this  material  as  a simple 
homogeneous  compound  or  as  a mixture  of  such 
compounds  is  absolutely  fallacious.  Protoplasm 
is  to-day  known  to  be  made  up  of  parts  harmoni- 
ously adapted  to  each  other  in  such  a way  as  to 
form  an  extraordinarily  intricate  machine;  and  the 
microscopist  of  to-day  recognizes  clearly  that  the 

activities  of  this 
material  must  be 
regarded  as  the 
result  of  the 
machinery  which 
makes  up  pro- 
toplasm rather 
than  as  the  sim- 
ple result  of  its 
chemical  com- 
position. Proto- 
plasm is  a ma- 
chine and  not  a 
chemical  com- 
pound. 

Structure  of 
Protoplasm.— 

The  structure  of 
protoplasm  isnot 
yet  thoroughly 
understood  by 
scientists,  but  a 
few  general  facts  are  known  beyond  question.  It 
is  thought,  in  the  first  place,  that  it  consists  of 


Fig.  23. — A cell  as  it  appears  to  the  modern 
microscope,  a , protoplasmic  reticulum  ; 
b , liquid  in  its  meshes  ; c , nuclear  mem- 
brane ; d , nuclear  reticulum  ; e,  chro- 
matin reticulum  ; f,  nucleolus  ; g,  cen- 
trosome  ; h , centrosphere  ; i,  vacuole  ; 
j,  inert  bodies. 


THE  CELL  AND  PROTOPLASM. 


87 


two  quite  different  substances.  There  is  a some- 
what solid  material  permeating  it,  usually,  regarded 
as  having  a reticulate  structure.  It  is  variously 
described,  sometimes  as  a reticulate  network, 
sometimes  as  a mass  of  threads  or  fibres,  and 
sometimes  as  a mass  of  foam  (Fig.  23,  a).  It  is 
extremely  delicate  and  only  visible  under  special 
conditions  and  with  the  best  of  microscopes.  Only 
under  peculiar  conditions  can  it  be  seen  in  proto- 
plasm while  alive.  There  is  no  question,  however, 
that  all  protoplasm  is  permeated  when  alive  by  a 
minute  delicate  mass  of  material,  which  may  take 
the  form  of  threads  or  fibres  or  may  assume  other 
forms.  Within  the  meshes  of  this  thread  or  retic- 
ulum there  is  found  a liquid,  perfectly  clear  and 
transparent,  to  whose  presence  the  liquid  charac- 
ter of  the  protoplasm  is  due  (Fig.  23,  b).  In  this 
liquid  no  structure  can  be  determined,  and,  so  far 
as  we  know,  it  is  homogeneous.  Still  further  study 
discloses  other  complexities.  It  appears  that  the 
fibrous  material  is  always  marked  by  the  presence 
of  excessively  minute  bodies,  which  have  been 
called  by  various  names,  but  which  we  will  speak 
of  as  microsomes.  Sometimes,  indeed,  the  fibres 
themselves  appear  almost  like  strings  of  beads, 
so  that  they  have  been  described  as  made  up 
of  rows  of  minute  elements.  It  is  immaterial 
for  our  purpose,  however,  whether  the  fibres 
are  to  be  regarded  as  made  up  of  microsomes 
or  not.  This  much  is  sure,  that  these  microsomes 
— granules  of  excessive  minuteness — occur  in 
protoplasm  and  are  closely  connected  with  the 
fibres  (Fig.  23,  a). 

The  Nucleus. — (a)  Presence  of  a Nucleus . — If 
protoplasm  has  thus  become  a new  substance  in 
our  minds  as  the  result  of  the  discoveries  of  the  last 
7 


88  THE  STORY  OF  THE  LIVING  MACHINE. 

twenty  years,  far  more  marvelous  have  been  the 
discoveries  made  in  connection  with  that  body 
which  has  been  called  the  nucleus.  Even  by  the 
early  microscopists  the  nucleus  was  recognized, 
and  during  the  first  few  years  of  the  cell  doctrine 
it  was  frequently  looked  upon  as  the  most  active 
part  of  the  cell  and  as  especially  connected  with 
its  reproduction.  The  doctrine  of  protoplasm, 
however,  so  captivated  the  minds  of  biologists  that 
for  quite  a number  of  years  the  nucleus  was  ig- 
nored, at  least  in  all  discussions  connected  with 
the  nature  of  life.  It  was  a body  in  the  cell  whose 
presence  was  unexplained  and  which  did  not  fall 
into  accord  with  the  general  view  of  protoplasm 
as  the  physical  basis  of  life.  For  a while,  there- 
fore, biologists  gave  little  attention  to  it,  and  were 
accustomed  to  speak  of  it  simply  as  a bit  of 
protoplasm  a little  more  dense  than  the  rest.  The 
cell  was  a bit  of  protoplasm  with  a small  piece 
of  more  dense  protoplasm  in  its  centre  appearing 
a little  different  from  the  rest  and  perhaps  the 
most  active  part  of  the  cell. 

As  a result  of  this  excessive  belief  in  the  effi- 
ciency of  protoplasm  the  question  of  the  presence 
of  a nucleus  in  the  cell  was  for  a while  looked 
upon  as  one  of  comparatively  little  importance. 
Many  cells  were  found  to  have  nucleii  while  others 
did  not  show  their  presence,  and  microscopists 
therefore  believed  that  the  presence  of  a nucleus 
was  not  necessary  to  constitute  a cell.  A German 
naturalist  recognized  among  lower  animals  one 
group  whose  distinctive  characteristic  was  that 
they  were  made  of  cells  without  nucleii,  giving 
the  name  Monera  to  the  group.  As  the  method 
of  studying  cells  improved  microscopists  learned 
better  methods  of  discerning  the  presence  of  the 


THE  CELL  AND  PROTOPLASM. 


89 

nucleus,  and  as  it  was  done  little  by  little  they 
began  to  find  the  presence  of  nucleii  in  cells  in 
which  they  had  hitherto  not  been  seen.  As  micro- 
scopists  now  studied  one  after  another  of  these 
animals  and  plants  whose  cells  had  been  said  to 
contain  no  nucleus,  they  began  to  find  nucleii  in 
them,  until  the  conclusion  was  finally  reached  that 
a nucleus  is  a fundamental  part  of  all  active  cells. 
Old  cells  which  have  lost  their  activity  may  not 
show  nucleii,  but, 
so  far  as  we  know, 
all  activecells  pos- 
sess these  struc- 
tures, and  appar- 
ently no  cell  can 
carry  on  its  activ- 
ity without  them. 

Some  cells  have 
several  nucleii, 
and  others  have 
the  nuclear  matter 
scattered  through 
the  whole  cell  in- 
stead of  being  ag- 
gregated into  a 
mass ; but  nuclear 
matter  the  cell 
must  have  to 
carry  on  its  life. 

Later  the  experiment  was  made  of  depriving 
cells  of  their  nucleii,  and  it  still  further  empha- 
sized the  importance  of  the  nucleus.  Among  uni- 
cellular animals  are  some  which  are  large  enough 
for  direct  manipulation,  and  it  is  found  that  if 
these  cells  are  cut  into  pieces  the  different  pieces 

will  behave  very  differently  in  accordance  with 


Fig.  24. — A cell  cut  into  three  pieces,  each 
containing  a bit  of  the  nucleus.  Each 
continues  its  life  indefinitely,  soon  ac- 
quiring the  form  of  the  original  as  at  C. 


THE  STORY  OF  THE  LIVING  MACHINE. 


whether  or  not  they  have  within  them  a piece  of 
the  nucleus.  All  the  pieces  are  capable  of  carry- 
ing on  their  life  activities  for  a while.  The  pieces 
of  the  cell  which  contain  the  nucleus  of  the  origi- 
nal cell,  or  even  a part  of  it,  are  capable  of  carrying 

on  all  its  life  ac- 
tivities perfectly 
well.  InFig.  24is 
shown  such  a cell 
cut  into  three 
pieces,  each  of 
which  contains 
a piece  of  the 
nucleus.  Each 
carries  on  its  life 
activities,  feeds, 
grows  and  mul- 
tiplies perfectly 
well,  the  life  pro- 
cesses seeming  to 
continue  as  if 
nothing  had  hap- 
pened. Quitedif- 
ferent  is  it  with 
fragments  which 
contain  none  of 
the  nucleus  (Fig. 
25).  These  frag- 
ments (1  and  3), 
even  though  they 
may  be  com- 
paratively large  masses  of  protoplasm,  are  incap- 
able of  carrying  on  the  functions  of  their  life 
continuously.  For  a while  they  continue  to  move 
around  and  apparently  act  like  the  other  frag- 
ments, but  after  a little  their  life  ceases.  They 


Fig.  25. — A cell  cut  into  three  pieces,  only 
one  of  which,  No.  2,  contains  any 
nucleus.  This  fragment  soon  acquires 
the  original  form  and  continues  its  life 
indefinitely,  as  shown  at  B.  The  other 
two  pieces  though  living  for  a time, 
die  without  reproducing. 


THE  CELL  AND  PROTOPLASM.  91 

are  incapable  of  assimilating  food  and  incapable 
of  reproduction,  and  hence  their  life  cannot  con- 
tinue very  long.  Facts  like  these  demonstrate 
conclusively  the  vital  importance  of  the  nucleus 
in  cell  activity,  and  show  us  that  the  cell,  with  its 
power  of  continued  life,  must  be  regarded  as  a 
combination  of  protoplasm  with  its  nucleus,  and 
cannot  exist  without  it.  It  is  not  protoplasm, 
but  cell  substance,  plus  cell  nucleus,  which  forms 
the  simplest  basis  of  life. 

As  more  careful  study  of  protoplasm  was 
made  it  soon  became  evident  that  there  is  a 
very  decided  difference  between  the  nucleus  and 
the  protoplasm.  The  old  statement  that  the 
nucleus  is  simply  a bit  of  dense  protoplasm  is  not 
true.  In  its  chemical  and  physical  composition 
as  well  as  in  its  activities  the  nucleus  shows  itself 
to  be  entirely  different  from  the  protoplasm.  It 
contains  certain  definite  bodies  not  found  in  the 
cell  substance,  and  it  goes  through  a series  of 
activities  which  are  entirely  unrepresented  in  the 
surrounding  protoplasm.  It  is  something  entirely 
distinct,  and  its  relations  to  the  life  of  the  cell  are 
unique  and  marvelous.  These  various  facts  led 
to  a period  in  the  discussion  of  biological  topics 
which  may  not  inappropriately  be  called  the 
Reign  of  the  Nucleus.  Let  us,  therefore,  see  what 
this  structure  is  which  has  demanded  so  much 
attention  in  the  last  twenty  years. 

(b)  Structure  of  the  Nucleus. — At  first  the  nu- 
cleus appears  to  be  very  much  like  the  cell  sub- 
stance. Like  the  latter,  it  is  made  of  fibres,  which 
form  a reticulum  (Fig.  23),  and  these  fibres,  like 
those  of  protoplasm,  have  microsomes  in  intimate 
relation  with  them  and  hold  a clear  liquid  in  their 
meshes.  The  meshes  of  the  network  are  usually 


92  THE  STORY  OF  THE  LIVING  MACHINE. 

rather  closer  than  in  the  outer  cell  substance,  but 
their  general  character  appears  to  be  the  same. 
But  a more  close  study  of  the  nucleus  discloses 
vast  differences.  In  the  first  place,  the  nucleus  is 
usually  separated  from  the  cell  substance  by  a 
membrane  (Fig.  23,  c).  This  membrane  is  almost 
always  present,  but  it  may  disappear,  and  usually 
does  disappear,  when  the  nucleus  begins  to  divide. 
Within  the  nucleus  we  find  commonly  one  or  two 
smaller  bodies,  the  nucleoli  (Fig.  23,  /).  They 
appear  to  be  distinct  vital  parts  of  the  nucleus, 
and  thus  different  from  certain  other  solid  bodies 
which  are  simply  excreted  material,  and  hence 
lifeless.  Further,  we  find  that  the  reticulum 
within  the  nucleus  is  made  up  of  two  very  differ- 
ent parts.  One  portion  is  apparently  identical  with 
the  reticulum  of  the  cell  substance  (Fig.  23,  d). 
This  forms  an  extremely  delicate  network,  whose 
fibres  have  chemical  relations  similar  to  those  of 
the  cell  substance.  Indeed,  sometimes,  the  fibres 
of  the  nucleus  may  be  seen  to  pass  directly  into 
those  of  the  network  of  the  cell  substance,  and 
hence  they  are  in  all  probability  identical.  This 
material  is  called  linin , by  which  name  we  shall 
hereafter  refer  to  it.  There  is,  however,  in  the  nu- 
cleus another  material  which  forms  either  threads, 
or  a network,  or  a mass  of  granules,  which  is  very 
different  from  the  linin,  and  has  entirely  different 
properties.  This  network  has  the  power  of  ab- 
sorbing certain  kinds  of  stains  very  actively, 
and  is  consequently  deeply  stained  when  treated 
as  the  microscopist  commonly  prepares  his  speci- 
mens. For  this  reason  it  has  been  named  chro- 
matin (Fig,  23,  e),  although  in  more  recent  times 
other  names  have  been  given  to  it.  Of  all  parts 
pf  the  cell  this  chromatin  is  the  most  remarkable. 


THE  CELL  AND  PROTOPLASM. 


93 


It  appears  in  great  variety  in  different  cells,  but 
it  always  has  remarkable  physiological  properties, 
as  will  be  noticed  presently.  All  things  consid- 
ered, this  chromatin  is  probably  the  most  remark- 
able body  connected  with  organic  life. 

The  nucleii  of  different  animals  and  plants  all 
show  essentially  the  characteristics  just  described. 
They  all  contain  a liquid,  a linin  network,  and  a 
chromatin  thread  or  network,  but  they  differ  most 
remarkably  in  details,  so  that  the  variety  among 


the  nucleii  is  almost  endless  (Fig.  26).  They  differ 
first  in  their  size  relative  to  the  size  of  the  cell ; 
sometimes — especially  in  young  cells — the  nucleus 
being  very  large,  while  in  other  cases  the  nucleus 
is  very  small  and  the  protoplasmic  contents  of  the 
cell  very  large;  finally,  in  cells  which  have  lost 
their  activity  the  nucleus  may  almost  or  entirely 
disappear.  They  differ,  secondly,  in  shape.  The 
typical  form  appears  to  be  spherical  or  nearly  so; 


94 


THE  STORY  OF  THE  LIVING  MACHINE. 


but  from  this  typical  form  they  may  vary,  becom- 
ing irregular  or  elongated.  They  are  sometimes 
drawn  out  into  long  masses  looking  like  a string 
of  beads  (Fig.  24),  or,  again,  resembling  minute 
coiled  worms  (Fig.  21),  while  in  still  other  cells 
they  may  be  branching  like  the  twigs  of  a tree. 
The  form  and  shape  of  the  chromatin  thread  dif- 
fers widely.  Sometimes  this  appears  to  be  mere 
reticulum  (Fig.  23) ; at  others,  a short  thread  which 
is  somewhat  twisted  or  coiled  (Fig.  26)  ; while 
in  other  cells  the  chromatin  thread  is  an  extremely 
long,  very  much  twisted  convolute  thread  so  com- 
plexly woven  into  a tangle  as  to  give  the  appear- 
ance of  a minute  network.  The  nucleii  differ  also 
in  the  number  of  nucleoli  they  contain  as  well  as 
in  other  less  important  particulars.  Fig.  26  will 
give  a little  notion  of  the  variety  to  be  found 
among  different  nucleii;  but  although  they  thus 
do  vary  most  remarkably  in  shape  in  the  essential 
parts  of  their  structure  they  are  alike. 

Centrosome. — Before  noticing  the  activities  of 
the  nucleus  it  will  be  necessary  to  mention  a third 
part  of  the  cell.  Within  the  last  few  years  there 
has  been  found  to  be  present  in  most  cells  an 
organ  which  has  been  called  the  centrosome.  This 
body  is  shown  at  Fig.  23,  g.  It  is  found  in  the 
cell  substance  just  outside  the  nucleus,  and  com- 
monly appears  as  an  extremely  minute  rounded 
dot,  so  minute  that  no  internal  structure  has  been 
discerned.  It  may  be  no  larger  than  the  minute 
granules  or  microsomes  in  the  cell,  and  until 
recently  it  entirely  escaped  the  notice  of  micro- 
scopists.  It  has  now,  however,  been  clearly 
demonstrated  as  an  active  part  of  the  cell  and 
entirely  distinct  from  the  ordinary  microsomes. 
It  stains  differently,  and,  as  we  shall  soon  see,  it 


THE  CELL  AND  PROTOPLASM.  95 

appears  to  be  in  most  intimate  connection  with 
the  center  of  cell  life.  In  the  activities  which 
characterize  cell  life  this  centrosome  appears  to 
lead  the  way.  From  it  radiate  the  forces  which 
control  cell  activity,  and  hence  this  centrosome  is 
sometimes  called  the  dynamic  center  of  the  cell. 
This  leads  us  to  the  study  of  cell  activity,  which 
discloses  to  us  some  of  the  most  extraordinary 
phenomena  which  have  come  to  the  knowledge 
of  science. 

Function  of  the  Nucleus. — To  understand  why 
it  is  that  the  nucleus  has  taken  such  a prominent 
position  in  modern  biological  discussion  it  will  be 
only  necessary  to  notice  some  of  the  activities 
of  the  cell.  Of  the  four  fundamental  vital  prop- 
erties of  cell  life  the  one  which  has  been  most 
studied  and  in  regard  to  which  most  is  known  is 
reproduction.  This  knowledge  appears  chiefly  un- 
der two  heads,  viz.,  cell  division  and  the  fertilization 
of  the  egg.  Every  animal  and  plant  begins  its 
life  as  a simple  cell,  and  the  growth  of  the  cell 
into  the  adult  is  simply  the  division  of  the  original 
cell  into  parts  accompanied  by  a differentiation 
of  the  parts.  The  -fundamental  phenomena  of 
growth  and  reproduction  is  thus  ceil  division, 
and  if  we  can  comprehend  this  process  in  these 
simple  cells  we  shall  certainly  have  taken  a great 
step  toward  the  explanation  of  the  mechanics  of 
life.  During  the  last  ten  years  this  cell  division 
has  been  most  thoroughly  studied,  and  we  have 
a pretty  good  knowledge  of  it  so  far  as  its 
microscopical  features  are  concerned.  The  fol- 
lowing description  will  outline  the  general  facts 
of  such  cell  division,  and  will  apply  with  consid- 
erable accuracy  to  all  cases  of  cell  division,  al- 
though the  details  may  differ  not  a little. 


9 6 THE  STORY  OF  THE  LIVING  MACHINE. 

Cell  Division  or  Karyokinesis. — We  will  begin 
with  a ceil  in  what  is  called  the  resting  stage, 
shown  at  Fig.  23.  Such  a cell  has  a nucleus,  with 
its  chromatin,  its  membrane,  and  linin,  as  already 
described.  Outside  the  nucleus  is  the  centrosome, 
or,  more  commonly,  two  of  them  lying  close  to- 
gether. If  there  is  only  one  it  soon  divides  into 
two,  and  if  it  has  already  two,  this  is  because  a 
single  centrosome  which  the  cell  originally  pos- 
sessed has  already  divided  into  two,  as  we  shall 
presently  see.  This  cell,  in  short,  is  precisely  like 
the  typical  cell  which  we  have  described,  except 
in  the  possession  of  two  centrosomes.  The  first 


Fig.  27. — This  and  the  following  figures  show  stages  in  cell  divi- 
sion. Fig.  27  shows  the  resting  stage  with  the  chromatin,  cr , 
in  the  form  of  a network  within  the  nuclear  membrane  and 
the  centrosome,  ce , already  divided  into  two. 

Fig.  28. — The  chromatin  is  broken  into  threads  or  chromosomes,  cr. 
The  centrosomes  show  radiating  fibres. 

indication  of  the  cell  division  is  shown  by  the 
chromatin  fibres.  During  the  resting  stage  this 
chromatin  material  may  have  the  form  of  a 
thread,  or  may  form  a network  of  fibres  (see  Fig. 
27).  But  whatever  be  its  form  during  the  resting 


THE  CELL  AND  PROTOPLASM.  97 

stage,  it  assumes  the  form  of  a thread  as  the  cell 
prepares  for  division.  Almost  at  once  this  thread 
breaks  into  a number  of  pieces  known  as  chromo- 
somes (Fig.  28).  It  is  an  extremely  important  fact 
that  the  number  of  these  chromosomes  in  the  ordi- 
nary cells  of  any  animal  or  plant  is  always  the  same. 
In  other  words,  in  all  the  cells  of  the  body  of  ani- 
mal or  plant  the  chromatin  material  in  the  nucleus 
breaks  into  the  same  number  of  short  threads  at 
the  time  that  the  cell  is  preparing  to  divide.  The 
number  is  the  same  for  all  animals  of  the  same 
species,  and  is  never  departed  from.  For  example, 
the  number  in  the  ox  is  always  sixteen,  while  the 
number  in  the  lily  is  always  twenty-four.  During 
this  process  of  the  formation  of  the  chromosomes 
the  nucleoli  disappear,  sometimes  being  absorbed 
apparently  in  the  chromosomes,  and  sometimes 
being  ejected  into  the  cell  body,  where  they  dis- 
appear. Whether  they  have  anything  to  do  with 
further  changes  is  not  yet  known. 

The  next  step  in  the  process  of  division  ap- 
pears in  the  region  of  the  centrosomes.  Each 
of  the  two  centrosomes  appears  to  send  out  from 
itself  delicate  radiating  fibres  into  the  surround- 
ing cell  substance  (Fig.  28).  Whether  these 
actually  arise  from  the  centrosome  or  are  simply 
a rearrangement  of  the  fibres  in  the  cell  sub- 
stance is  not  clear,  but  at  all  events  the  centro- 
some becomes  surrounded  by  a mass  of  radiating 
fibres  which  give  it  a starlike  appearance,  or, 
more  commonly,  the  appearance  of  a double  star, 
since  there  are  two  centrosomes  close  together 
(Fig.  28).  These  radiating  fibres,  whether  arising 
from  the  centrosomes  or  not,  certainly  all  centre 
in  these  bodies,  a fact  which  indicates  that  the 
centrosomes  contain  the  forces  which  regulate 


98  THE  STORY  OF  THE  LIVING  MACHINE. 


their  appearance.  Between  the  two  stars  or 
asters  a set  of  fibres  can  be  seen  running  from 
one  to  the  other  (Fig.  29).  These  two  asters  and 
the  centrosomes  within  them  have  been  spoken 
of  as  the  dynamic  centre  of  the  cell  since  they 
appear  to  control  the  forces  which  lead  to  cell 
division.  In  all  the  changes  which  follow  these 
asters  lead  the  way.  The  two  asters,  with  their 
centrosomes,  now  move  away  from  each  other, 
always  connected  by  the  spindle  fibres,  and  finally 
come  to  lie  on  opposite  sides  of  the  nucleus  (Figs. 


fibres. 

Fig.  30.— The  centrosomes  are  separate  and  the  equatorial  plate  of 
chromosomes,  or,  is  between  them. 

29,  30).  When  they  reach  this  position  they  are 
still  surrounded  by  the  radiating  fibres,  and  con- 
nected by  the  spindle  fibres.  Meantime  the  mem- 
brane around  the  nucleus  has  disappeared,  and 
thus  the  spindle  fibres  readily  penetrate  into  the 
nuclear  substance  (Fig.  30). 

During  this  time  the  chromosomes  have  been 
changing  their  position.  Whether  this  change  in 
position  is  due  to  forces  within  themselves,  or 
whether  they  are  moved  around  passively  by 
forces  residing  in  the  cell  substances,  or  whether, 


THE  CELL  AND  PROTOPLASM.  99 

which  is  the  most  probable,  they  are  pulled  or 
pushed  around  by'  the  spindle  fibres  which  are 
forcing  their  way  into  the  nucleus,  is  not  posi- 
tively known  ; nor  is  it,  for  our  purposes,  of  special 
importance.  At  all  events,  the  result  is  that  when 
the  asters  have  assumed  their  position  at  oppo- 
site poles  of  the  nucleus  the  chromosomes  are  ar- 
ranged in  a plane  passing  through  the  middle  of 
the  nucleus  at  equal  distances  from  each  aster. 
It  seems  certain  that  they  are  pulled  or  pushed  into 
this  position  by  forces  radiating  from  the  centro- 
somes.  Fig.  30  shows  this  central  arrangement 
of  the  chromosomes,  forming  what  is  called  the 
equatorial  plate. 

The  next  step  is  the  most  significant  of  all. 
It  consists  in  the  splitting  of  each  chromosome 
into  two  equal  halves.  The  threads  do  not  divide 
in  their  middle  but  split  lengthwise,  so  that  there  are 
formed  two  halves  identical  in  every  respect.  In 
this  way  are  produced  twice  the  original  num- 
ber of  chromosomes,  but  all  in  pairs.  The  pe- 
riod at  which  this  splitting  of 'the  chromosomes 
occurs  is  not  the  same  in  all  cells.  It  may  oc- 
cur, as  described,  at  about  the  time  the  asters 
have  reached  the  opposite  poles  of  the  nucleus, 
and  an  equatorial  plate  is  formed.  It  is  not  in- 
frequent, however,  for  it  to  occur  at  a period  con- 
siderably earlier,  so  that  the  chromosomes  are 
already  divided  when  they  are  brought  into  the 
equatorial  plate. 

At  some  period  or  other  in  the  cell  division 
this  splitting  of  the  chromosomes  takes  place. 
The  significance  of  the  splitting  is  especially  note- 
worthy. We  shall  soon  find  reason  for  believing 
that  the  chromosomes  contain  all  the  hereditary 
traits  which  the  cell  hands  down  from  generation 


IOO  THE  STORY  OF  THE  LIVING  MACHINE. 

to  generation,  and  indeed  that  the  chromosomes 
of  the  egg  contain  all  the  traits  which  the  parent 
hands  down  to  the  child.  Now,  if  this  chromatin 
thread  consists  of  a series  of  units,  each  repre- 
senting certain  hereditary  characters,  then  it  is 
plain  that  the  division  of  the  thread  by  splitting' 
will  give  rise  to  a double  series  of  threads,  each 
of  which  has  identical  characters.  Should  the 
division  occur  across  the  thread  the  two  halves 
would  be  unlike,  but  taking  place  as  it  does  by  a 
longitudinal  splitting  each  unit  in  the  thread  sim- 
ply divides  in  half,  and  thus  the  resulting  half 
threads  each  contain  the  same  number  of  similar 
units  as  the  other  and  the  same  as  possessed  by 
the  original  undivided  chromosome.  This  sort  of 
splitting  thus  doubles  the  number  of  chromo- 
somes, but  produces  no  differentiation  of  material. 


Fig.  31.  Fig.  32. 

Fig.  31. — Stage  showing  the  two  halves  of  the  chromosomes  sepa- 
rated from  each  other. 

Fig.  32. — Final  stage  with  two  nucleii  in  which  the  chromosomes 
have  again  assumed  the  form  of  a network.  The  centrosomes 
have  divided  preparatory  to  the  next  division,  and  the  cell  is 
beginning  to  divide. 

The  next  step  in  the  cell  division  consists  in 
the  separation  of  the  two  halves  of  the  chromo- 
somes. Each  half  of  each  chromosome  separates 


THE  CELL  AND  PROTOPLASM. 


IOI 


from  its  fellow,  and  moves  to  the  opposite  end  of 
the  nucleus  toward  the  two  centrosomes  (Fig. 
31).  Whether  they  are  pulled  apart  or  pushed 
apart  by  the  spindle  fibres  is  not  certain,  although 
it  is  apparently  sure  that  these  fibres  from  the 
centrosomes  are  engaged  in  the  matter.  Certain 
it  is  that  some  force  exerted  from  the  two  centro- 
somes acts  upon  the  chromosomes,  and  forces  the 
two  halves  of  each  one  to  opposite  ends  of  the 
nucleus,  where  they  now  collect  and  form  two  neiv 
nucleii , with  evidently  exactly  the  same  number  of 
chromosomes  as  the  original,  and  with  charac- 
ters identical  to  each  other  and  to  the  original 

(F'g-  32). 

The  rest  of  the  cell  division  now  follows  rap- 
idly. A partition  grows  in  through  the  cell  body 
dividing  it  into  two  parts  (Fig.  32),  the  division 
passing  through  the  middle  of  the  spindle.  In 
this  division,  in  some  cases  at  least,  the  spindle 
fibres  bear  a part — a fact  which  again  points  to 
the  importance  of  the  centrosomes  and  the  forces 
which  radiate  from  them.  Now  t'he  chromosomes 
in  each  daughter  nucleus  unite  to  form  a single 
thread,  or  may  diffuse  through  the  nucleus  to  form 
a network,  as  in  Fig.  32.  They  now  become  sur- 
rounded by  a membrane,  so  that  the  new  nucleus 
appears  exactly  like  the  original  one.  The 
spindle  fibres  disappear,  and  the  astral  fibres 
may  either  disappear  or  remain  visible.  The 
centrosome  may  apparently  in  some  cases  disap- 
pear, but  more  commonly  remains  beside  the 
daughter  nucleii,  or  it  may  move  into  the  nucleus. 
Eventually  it  divides  into  two,  the  division  com- 
monly occurring  at  once  (Fig.  32),  but  sometimes 
not  until  the  next  cell  division  is  about  to  begin. 
Thus  the  final  result  shows  two  cells  each  with  a 


102  THE  STORY  OF  THE  LIVING  MACHINE. 

nucleus  and  two  centrosomes,  and  this  is  exactly 
the  same  sort  of  structure  with  which  the  process 
began.  [See  Frontispiece .) 

Viewed  as  a whole,  we  may  make  the  follow- 
ing general  summary  o£  this  process.  The  essen- 
tial object  of  this  complicated  phenomena  of 
karyokinesis  is  to  divide  the  chromatin  into  equiv- 
alent halves,  so  that  the  cells  resulting  from  the 
cell  division  shall  contain  an  exactly  equivalent 
chromatin  content.  For  this  purpose  the  chro- 
matic elements  collect  into  threads  and  split 
lengthwise.  The  centrosome,  with  its  fibres, 
brings  about  the  separation  of  these  two  halves. 
Plainly,  we  must  conclude  that  the  chromatin  ma- 
terial is  something  of  extraordinary  importance 
to  the  cell,  and  the  centrosome  is  a bit  of  ma- 
chinery for  controlling  its  division  and  thus  regu- 
lating cell  division. 

Fertilization  of  the  Egg. — This  description  of 
cell  division  will  certainly  give  some  idea  of  the 
complexity  of  cell  life,  but  a more  marvelous  se- 
ries of  changes  still  takes  place  during  the  time 
when  the  egg  is  preparing  for  development.  In- 
asmuch as  this  process  still  further  illustrates  the 
nature  of  the  cell,  and  has  further  a most  intimate 
bearing  upon  the  fundamental  problem  of  hered- 
ity, it  will  be  necessary  for  us  to  consider  it  here 
briefly. 

The  sexual  reproduction  of  the  many-celled 
animals  is  always  essentially  alike.  A single  one 
of  the  body  cells  is  set  apart  to  start  the  next 
generation,  and  this  cell,  after  separating  from  the 
body  of  the  animal  or  plant  which  produced  it, 
begins  to  divide,  as  already  shown  in  Fig.  8, 
and  the  many  cells  which  arise  from  it  eventually 
form  the  new  individual.  This  reproductive  cell 


THE  CELL  AND  PROTOPLASM. 


103 


' ’rLvL:;-^ 


is  the  egg.  But  before  its  division  can  begin 
there  occurs  in  all  cases  of  sexual  reproduction  a 
process  called  fertilization,  the  essential  feature 
of  which  is  the  union  of  this  cell  with  another 
commonly  from  a different  individual.  While  the 
phenomenon  is  subject  to  considerable  difference 
in  details,  it  is  essentially  as  follows: 

The  female  reproductive  cell  is  called  the  egg, 
and  it  is  this  cell  which  divides  to  form  the  next 
generation.  Such  a cell  is  shown  in  Fig.  33. 
Like  other  cells  it 
has  a cell  wall,  a 
cell  substance  with 
its  linin  and  fluid 
portions,  a nucleus 
surrounded  by  a 
membrane  and  con- 
taining a reticulum, 
a nucleolus  and 
chromatic  mate- 
rial, and  lastly,  a 
centrosome.  Now 
such  an  egg  is  a 
complete  cell,  but 
it  is  not  able  to 
begin  the  process 
of  division  which 
shall  give  rise  to  a 
new  individual  until  it  has  united  with  another  cell 
of  quite  a different  sort  and  commonly  derived  from 
a different  individual  called  the  male.  Why  the 
egg  cell  is  unable  to  develop  without  such  union 
with  male  cell  does  not  concern  us  here,  but  its 
purpose  will  be  evident  as  the  description  pro- 
ceeds. The  egg  cell  as  it  comes  from  the  ovary 
of  the  female  individual  is,  however,  not  yet  ready 
8 


Fig.  33. — An  egg  showing  the  cell  sub- 
stance, and  the  nucleus,  the  latter 
containing  chromosomes  in  large 
number  and  a nucleolus. 


104  the  story  of  the  living  machine. 

for  union  with  the  male  cell,  but  must  first  go 
through  a series  of  somewhat  remarkable  changes 
constituting  what  is  called  maturation  of  the  egg. 
This  phenomenon  has  such  an  intimate  relation 
to  all  problems  connected  with  the  cell,  that  it 
must  be  described  somewhat  in  detail.  There 
are  considerable  differences  in  the  details  of  the 
process  as  it  occurs  in  various  animals,  but  they 
all  agree  in  the  fundamental  points.  The  follow- 
ing is  a general  description  of  the  process  derived 
from  the  study  of  a large  variety  of  animals  and 
plants. 

In  the  cells  of  the  body  of  the  animal  to 
which  this  description  applies  there  are  four  chro- 


Fig.  34. — This  and  the  following  figures  represent  the  process  of 
fertilization  of  an  egg.  In  all  figures  cr  is  the  chromosomes  ; 
cs  represents  the  cell  substance  (omitted  in  the  following 
figures) ; me  is  the  male  reproductive  cell  lying  in  contact  with 
the  egg ; mn  is  the  male  nucleus  after  entering  the  egg. 

Fig.  35. — The  egg  centrosome  has  divided,  and  the  male  cell  with 
its  centrosome  has  entered  the  egg. 


mosomes.  This  is  true  of  all  the  cells  of  the  ani- 
mal except  the  sexual  cells.  The  eggs  arise  from 
the  other  cells  of  the  body,  but  during  their 


THE  CELL  AND  PROTOPLASM.  105 

growth  the  chromatin  splits  in  such  a way  that 
the  egg  contains  double  the  number  of  chromo- 
somes, i.  e.,  eight  (Fig.  34).  If  this  egg  should 
now  unite  with  the  other  reproductive  cell  from 
the  male,  the  resulting  fertilized  egg  would  plain- 
ly contain  a number  of  chromosomes  larger  than 
that  normal  for  this  species  of  animal.  As  a re- 
sult the  next  generation  would  have  a larger  num- 
ber of  chromosomes  in  each  cell  than  the  last 
generation,  since  the  division  of  the  egg  in  devel- 
opment is  like  that  already  described,  and  always 
results  in  producing  new  cells  with  the  same 
number  of  chromosomes  as  the  starting  cell. 
Hence,  if  the  number  of  chromosomes  in  the  next 
generation  is  to  be  kept  equal  to  that  in  the  last 


Fig.  36.  Fig.  37. 

Fig.  36. — The  egg*  centrosomes  have  changed  their  position.  The 
male  cell  with  its  centrosome  remains  inactive  until  the  stage 
represented  in  Fig.  42. 

Fig.  37. — Beginning  of  the  first  division  for  removing  superfluous 
chromosomes. 

generation,  this  egg  cell  must  get  rid  of  a part  of 
its  chromatin  material.  This  is  done  by  a process 
shown  in  Fig.  35.  The  centrosome  divides  as  in 
ordinary  cell  division  (Fig.  35),  and  after  rota- 
ting on  its  axis  it  approaches  the  surface  of  the 


10 6 THE  STORY  OF  THE  LIVING  MACHINE. 


egg  (Figs.  36  and  37).  The  egg  now  divides  (Fig. 
38),  but  the  division  is  of  a peculiar  kind.  Al- 
though the  chromosomes  divide  equally  the  egg 
itself  divides  into  two  very  unequal  parts,  one  part 
still  appearing  as  the  egg  and  the  other  as  a mi- 
nute protuberance  called  the  polar  cell  (pc'  in 
Fig.  38).  The  chromosomes  do  not  split  as  they 
do  in  the  cell  division  already  described,  but  each 
of  these  two  cells,  the  egg  and  the  polar  body, 
receives  four  chromosomes  (Fig.  38).  The  result 
is  that  the  egg  has  now  the  normal  number  of 
chromosomes  for  the  ordinary  cells  of  the  animal 
in  question.  But  this  is  still  too  many,  for  the 


Fig.  38.  Fig.  39. 


Fig.  40. 

Fig.  38. — First  division  complete  and  first  polar  cell  formed,  pc' 
Fig.  39. — Formation  of  the  second  polar  cell,  pc” . 

Fig.  40. — Completion  of  the  process  of  extrusion  of  the  chromatic 
material  \fn  shows  the  two  chromosomes  retained  in  the  egg 
forming  the  female  pronucleus.  The  centrosome  has  disap- 
peared. 

egg  is  soon  to  unite  with  the  male  cell  ; and  this 
male  cell,  as  we  shall  see,  is  to  bring  in  its  own 
quota  of  chromosomes.  Hence  the  egg  must  get 


THE  CELL  AND  PROTOPLASM.  107 

rid  of  still  more  of  its  chromatin  material.  Con- 
sequently, the  first  division  is  followed  by  a sec- 
ond (Fig.  39),  in  which  there  is  again  produced  a 
large  and  a small  cell.  This  division,  like  the 
first,  occurs  without  any  splitting  of  the  chromo- 
somes, one  half  of  the  remaining  chromosomes 
being  ejected  in  this  new  cell,  the  second  polar 
cell  (pc")  leaving  the  larger  cell,  the  egg,  with 
just  one  half  the  number  of  chromosomes  normal 
for  the  cells  of  the  animal  in  question.  Meantime 
the  first  pole  cell  has  also  divided,  so  that  we  have 
now,  as  shown  in  Fig.  40,  four  cells,  three  small 
and  one  large,  but  each  containing  one  half  the 
normal  number  of  chromosomes.  In  the  example 
figured,  four  is  the  normal  number  for  the  cells 
of  the  animal.  The  egg  at  the  beginning  of  the 
process  contained  eight,  but  has  now  been  re- 
duced to  two.  In  the  further  history  of  the  egg 
the  smaller  cells,  called  polar  cells , take  no  part, 
since  they  soon  disappear  and  have  nothing  to  do 
with  the  animal  which  is  to  result  from  the  fur- 
ther division  of  the  egg.  This  process  of  the 
formation  of  the  polar  cells  is  thus  simply  a device 
for  getting  rid  of  some  of  the  chromatin  material 
in  the  egg  cell,  so  that  it  may  unite  with  a second 
cell  without  doubling  the  normal  number  of  chro- 
mosomes. 

Previously  to  this  process  the  other  sexual 
cell,  the  spermatozoon , or  male  reproductive  cell, 
has  been  undergoing  a somewhat  similar  process. 
This  is  also  a true  cell  (Fig.  34,  me ),  although  it 
is  of  a decidedly  smaller  size  than  the  egg  and  of 
a very  different  shape.  It  contains  cell  sub- 
stance, a nucleus  with  chromosomes,  and  a cen- 
trosome,  the  number  of  chromosomes,  as  shown 
later,  being  however  only  half  that  normal  for 


108  THE  STORY  OF  THE  LIVING  MACHINE. 

the  ordinary  cells  of  the  animals.  The  study 
of  the  development  of  the  spermatozoon  shows 
that  it  has  come  from  ceils  which  contained  the 
normal  number  of  four,  but  that  this  number  has 
been  reduced  to  one  half  by  a process  which  is 
equivalent  to  that  which  we  have  just  noticed  in 
the  egg.  Thus  it  cbmes  about  that  each  of  the 
sexual  elements,  the  egg  and  the  spermatozoon, 
now  contains  one  half  the  normal  number  of 
chromosomes. 

Now  by  some  mechanical  means  these  two  re- 
productive cells  are  brought  in  contact  with  each 
other,  shown  in  Fig.  34,  and  as  soon  as  they  are 
brought  into  each  other’s  vicinity  the  male  cell 
buries  its  head  in  the  body  of  the  egg.  The  tail 
by  which  it  has  been  moving  is  cast  off,  and  the 
head  containing  the  chromosomes  and  the  centro- 
some  enters  the  egg,  forming  what  is  called  the 
male  pronucleus  (Fig.  35-38,  mn).  This  entrance 
of  the  male  cell  occurs  either  before  the  forma- 
tion of  the  polar  cells  of  the  egg  or  afterward. 
If,  however,  it  takes  place  before,  the  male  pronu- 
cleus simply  remains  dormant  in  the  egg  while 
the  polar  cells  are  being  protruded,  and  not  until 
after  that  process  is  concluded  does  it  begin 
again  to  show  signs  of  activity  which  result  in  the 
cell  union. 

The  further  steps  in  this  process  appear  to  be 
controlled  by  the  centrosome,  although  it  is  not 
quite  certain  whence  this  centrosome  is  derived. 
Originally,  as  we  have  seen,  the  egg  contained  a 
centrosome,  and  the  male  cell  has  also  brought 
a second  into  the  egg  (Fig.  35,  ce).  In  some 
cases,  and  this  is  true  for  the  worm  we  are  de- 
scribing, it  is  certain  that  the  egg  centrosome 
disappears  while  that  of  the  spermatozoon  is  re- 


THE  CELL  AND  PROTOPLASM.  109 

tained  alone  to  direct  the  further  activities  (Fig. 
41).  Possibly  this  may  be  the  case  in  all  eggs,  but 
it  is  not  sure.  It  is  a matter  of  some  little  inter- 
est to  have  this  settled,  for  if  it  should  prove  true, 
then  it  would  evidently  follow  that  the  machinery 
for  cell  division,  in  the  case  of  sexual  reproduc- 
tion, is  derived  from  the  father,  although  the  bulk 
of  the  cell  comes  from  the  mother,  while  the  chro- 
mosomes come  from  both  parents. 

In  the  cases  where  the  process  has  been  most 
carefully  studied,  the  further  changes  are  as  fol- 
lows: The  head  of  the  spermatozoon,  after  en- 
trance into  the  egg,  lies  dormant  until  the  egg  has 
thrown  off  its  polar  cells,  and  thus  gotten  rid  of 
part  of  its  chromosomes.  Close  to  it  lies  its  cen- 


Fig.  41.  Fig.  42. 

Fig.  41. — The  chromosomes  in  the  male  and  female  pronucleii  have 
resolved  into  a network.  The  male  centrosome  begins  to  show 
signs  of  activity. 

Fig.  42. — The  centrosome  has  divided,  and  the  two  pronucleii  ha\e 
been  brought  together.  The  network  in  each  nucleus  has 
again  resolved  itself  into  two  chromosomes  which  are  now 
brought  together  near  the  centre  of  the  egg  but  do  not  fuse ; 
mcr , represents  the  chromosomes  from  the  male  nucleus  ; fcr , 
the  chromosomes  from  the  female  nucleus. 

trosomes  (Fig.  35,  ce),  and  there  is  thus  formed 
What  is  known  as  the  male  pronucleus  (Fig.  35-40, 


no  THE  STORY  OF  THE  LIVING  MACHINE. 

mri).  The  remains  of  the  egg  nucleus,  after  hav- 
ing discharged  the  polar  cells,  form  the  female  nu- 
cleus (Fig.  40,  fn).  The  chromatin  material,  in 
both  the  male  and  female  pronucleus,  soon  breaks 
up  into  a network  in  which  it  is  no  longer  possible 
to  see  that  each  contains  two  chromosomes  (Fig. 

41) .  Now  the  centrosome,  which  is  beside  the 
male  pronucleus,  shows  signs  of  activity.  It  be- 
comes surrounded  by  prominent  rays  to  form  an 
aster  (Fig.  41 , ce),  and  then  it  begins  to  move 
toward  the  female  pronucleus,  apparently  drag- 
ging the  male  pronucleus  after  it.  In  this  way  the 
centrosome  approaches  the  female  pronucleus,  and 
thus  finally  the  two  nucleii  are  brought  into  close 
proximity.  Meantime  the  chromatin  material  in 
each  has  once  more  broken  up  into  short  threads 
or  chromosomes,  and  once  more  we  find  that  each 
of  the  nucleii  contains  two  of  these  bodies  (Fig. 

42) .  In  the  subsequent  figures  the  chromosomes 
of  the  male  nucleus  are  lightly  shaded,  while  those 
of  the  female  are  black  in  order  to  distinguish 
them.  As  these  two  nucleii  finally  come  together 
their  membranes  disappear,  and  the  chromatic  ma- 
terial comes  to  lie  freely  in  the  egg,  the  male  and 
female  chromosomes,  side  by  side,  but  distinct 
forming  the  segmentation  nucleus . The  egg  plainly 
now  contains  once  more  the  number  of  chromo- 
somes normal  for  the  cells  of  the  animal,  but 
half  of  them  have  been  derived  from  each  par- 
ent. It  is  very  suggestive  to  find  further  that 
the  chromosomes  in  this  fertilized  egg  do  not  fuse 
with  each  other,  but  remain  quite  distinct,  so  that 
it  can  be  seen  that  the  new  nucleus  contains  chro- 
mosomes derived  from  each  parent  (Fig.  42).  Nor 
does  there  appear  to  be,  in  the  future  history  of  this 
egg,  any  actual  fusion  of  the  chromatic  material, 


THE  CELL  AND  FROTOPLASM. 


HI 


the  male  and  female  chromosomes  perhaps  always 
remaining  distinct. 

While  this  mixture  of  chromosomes  has  been 
taking  place  the  centrosome  has  divided  into  two 
parts,  each  of  which  becomes  surrounded  by  an 
aster  and  travels  to  opposite  ends  of  the  nucleus 
(Fig.  42).  There  now  follows  a division  of  the 
nucleus  exactly  similar  to  that  which  occurs  in 
the  normal  cell  division  already  described  in  Figs. 
28-34.  Each  of  the  chromosomes  splits  length- 
wise (Fig.  43),  and  one  half  of  each  then  travels 
toward  each  centrosome  to  form  a new  nucleus 
(Fig.  44).  Since  each  of  the  four  chromosomes 


Fig.  43.  Fig.  44. 

Fig.  43. — An  equatorial  plate  is  fcrmed  and  each  chromosome  has 
split  into  two  halves  by  longititudinal  division. 

Fig.  44. — The  halves  of  the  chromosomes  have  separated  to  form 
two  nucleii,  each  with  male  and  female  chromosomes.  The  egg 
has  divided  into  two  cells. 


thus  splits,  it  follows  that  each  of  the  two  daugh- 
ter nucleii  will,  of  course,  contain  four  chromo- 
somes; two  of  which  have  been  derived  from  the 
male  and  two  from  the  female  parent.  From  now 
the  divisions  of  the  egg  follow  rapidly  by  the  nor- 
mal process  of  cell  division  until  from  this  one 
egg  cell  there  are  eventually  derived  hundreds  of 


1 12  THE  STORY  OF  THE  LIVING  MACHINE. 

thousands  of  cells  which  are  gradually  moulded 
into  the  adult.  All  of  these  cells  will,  of  course, 
contain  four  chromosomes ; and,  what  is  more  im- 
portant, half  of  the  chromosomes  will  have  been 
derived  directly  from  the  male  and  half  from  the 
female  parent.  Even  into  adult  life,  therefore,  the 
cells  of  the  animal  probably  contain  chromatin 
derived  by  direct  descent  from  each  of  its  parents. 

The  Significance  of  Fertilization. — From  this 
process  of  fertilization  a number  of  conclusions, 
highly  important  for  our  purpose,  can  be  drawn. 
In  the  first  place,  it  is  evident  that  the  chromo- 
somes form  the  part  of  the  cell  which  contain  the 
hereditary  traits  handed  down  from  parent  to 
child.  This  follows  from  the  fact  that  the  chro- 
mosomes are  the  only  part  of  the  cell  which,  inthe 
fertilized  egg,  is  derived  from  both  parents.  Now 
the  offspring  can  certainly  inherit  from  each  parent, 
and  hence  the  hereditary  traits  must  be  associated 
with  some  part  of  the  cell  which  is  derived  from 
both.  But  the  egg  substance  is  derived  from  the 
mother  alone ; the  centrosome,  at  least  in  some 
cases  and  perhaps  in  all,  is  derived  only  from  the 
father,  while  the  chromosomes  are  derived  from 
both  parents.  Hence  it  follows  that  the  hereditary 
traits  must  be  particularly  associated  with  the 
chromosomes. 

With  this  understanding  we  can,  at  least,  in 
part  understand  the  purpose  of  fertilization.  As 
we  shall  see  later,  it  is  very  necessary  in  the  build- 
ing of  the  living  machine  for  each  individual  to 
inherit  characters  from  more  than  one  individual. 
This  is  necessary  to  produce  the  numerous  varia- 
tions which  contribute  to  the  construction  of  the 
machine.  For  this  purpose  there  has  been  devel- 
oped the  process  of  sexual  union  of  reproductive 


THE  CELL  AND  PROTOPLASM.  113 

cells,  which  introduces  into  the  offspring  chro- 
matic material  from  two  parents.  But  if  the  two 
reproductive  cells  should  unite  at  once  the  num- 
ber of  chromosomes  would  be  doubled  in  each  gen- 
eration, and  hence  be  constantly  increasing.  To 
prevent  this  the  polar  cells  are  cast  out,  which  re- 
duces the  amount  of  chromatic  material.  The 
union  of  the  two  pronucleii  is  plainly  to  produce 
a nucleus  which  shall  contain  chromosomes,  and 
hence  hereditary  traits  from  each  parent  and  the 
subsequent  splitting  of  these  chromosomes  and 
the  separation  of  the  two  halves  into  daughter  nu- 
cleii  insures  that  all  the  nucleii,  and  hence  all  cells 
of  the  adult,  shall  possess  hereditary  traits  derived 
from  both  parents.  Thus  it  comes  that,  even  in 
the  adult,  every  body  cell  is  made  up  of  chromo- 
somes from  each  parent,  and  may  hence  inherit 
characters  from  each. 

The  cell  of  an  animal  thus  consists  of  three 
somewhat  distinct  but  active  parts — the  cell  sub- 
stance, the  chromosomes,  and  the  centrosome.  Of 
these  the  cell  substance  appears  to  be  handed 
down  from  the  mother;  the  centrosome  comes,  at 
least  in  some  cases,  from  the  father,  and  the  chro- 
mosomes from  both  parents.  It  is  not  yet  certain, 
however,  whether  the  centrosome  is  a constant 
part  of  the  cell.  In  some  cells  it  cannot  yet  be 
found,  and  there  are  some  reasons  for  believing 
that  it  may  be  formed  out  of  other  parts  of  the 
cell.  The  nucleus  is  always  a direct  descendant 
from  the  nucleus  of  pre-existing  cells,  so  that  there 
is  an  absolute  continuity  of  descent  between  the 
nucleii  of  the  cells  of  an  individual  and  those  of 
its  antecedents  back  for  numberless  generations. 
It  is  not  certain  that  there  is  any  such  continuity 
of  descent  in  the  case  of  the  centrosomes ; for, 


114  the  story  of  the  living  machine. 

while  in  the  process  of  fertilization  the  centro- 
some  is  handed  dowNn  from  parent  to  child,  there 
are  some  reasons  for  believing  that  it  may  dis- 
appear in  subsequent  cells,  and  later  be  redevel- 
oped out  of  other  parts.  The  only  part  of  the 
cell  in  which  complete  continuity  from  parent  to 
child  is  demonstrated,  is  the  nucleus  and  particu- 
larly the  chromosomes.  All  of  these  facts  simply 
emphasize  the  importance  of  the  chromosomes, 
and  tell  us  that  these  bodies  must  be  regarded  as 
containing  the  most  important  features  of  the  cell 
which  constitute  its  individuality. 

What  is  Protoplasm  ? — Enough  has  now  been 
given  of  disclosures  of  the  modern  microscope 
to  show  that  our  old  friend  Protoplasm  has  as- 
sumed an  entirely  new  guise,  if  indeed  it  has  not 
disappeared  altogether.  These  simplest  life  pro- 
cesses are  so  marvelous  and  involve  the  action  of 
such  an  intricate  mass  of  machinery  that  we  can 
no  longer  retain  our  earlier  notion  of  protoplasm 
as  the  physical  basis  of  life.  There  can  be  no 
life  without  the  properties  of  assimilation,  growth, 
and  reproduction  ; and,  so  far  as  we  know,  these 
properties  are  found  only  in  that  combination  of 
bodies  which  we  call  the  cell,  with  its  mixture  of 
harmoniously  acting  parts.  Life , at  least  the  life  of 
a cell , is  then  not  the  property  of  a chemical  compound 
protoplasm , but  is  the  result  of  the  activities  of  a ma- 
chine. Indeed,  we  are  now  at  a loss  to  know  how 
we  can  retain  the  term  protoplasm.  As  originally 
used  it  meant  the  contents  of  the  cell,  and  the  sig- 
nificance in  the  term  was  in  the  conception  of  pro- 
toplasm as  a somewhat  homogeneous  chemical 
compound  uniform  in  all  types  of  life.  But  we  now 
see  that  this  cell  contains  not  a single  substance, 
but  a large  number,  including  solids,  jelly  masses, 


THE  CELL  AND  PROTOPLASM. 


”5 


and  liquids,  each  of  which  has  its  own  chemical 
composition.  The  number  of  chemical  compounds 
existing  in  the  material  formerly  called  protoplasm 
no  one  knows,  but  we  do  know  that  they  are  many, 
and  that  the  different  substances  are  combined  to 
form  a physical  structure.  Which  of-these  various 
bodies  shall  we  continue  to  call  protoplasm  ? 
Shall  it  be  the  linin,  or  the  liquids,  or  the  micro- 
somes,  or  the  chromatin  threads,  or  the  centro- 
somes  ? Which  of  these  is  the  actual  physical 
basis  of  life?  From  the  description  of  cell  life 
which  we  have  given,  it  will  be  evident  that  no 
one  of  them  is  a material  upon  which  our  chemi- 
cal biologists  can  longer  found  a chemical  theory 
of  life.  That  chemical  theory  of  life,  as  we  have 
seen,  was  founded  upon  the  conception  that  the 
primitive  life  substance  is  a definite  chemical 
compound.  No  such  compound  has  been  dis- 
covered, and  these  disclosures  of  the  microscope 
of  the  last  few  years  have  been  such  as  to  lead 
us  to  abandon  hope  of  ever  discovering  such  a 
compound.  It  is  apparently  impossible  to  re- 
duce life  to  any  simpler  basis  than  this  combi- 
nation of  bodies  which  make  up  what  was  for- 
merly called  protoplasm.  The  term  protoplasm 
is  still  in  use  with  different  meanings  as  used  by 
different  writers.  Sometime  it  is  used  to  refer  to 
the  entire  contents  of  the  cell;  sometimes  to  the 
cell  substance  only  outside  the  nucleus.  Plainly, 
it  is  not  the  protoplasm  of  earlier  years. 

With  this  conclusion  one  of  our  fundamental 
questions  has  been  answered.  We  found  in  our 
first  chapter  that  the  general  activities  of  animals 
and  plants  are  easily  reduced  to  the  action  of  a 
machine,  provided  we  had  the  fundamental  vital 
powers  residing  in  the  parts  of  that  machine.  We 


II 6 THE  STORY  OF  THE  LIVING  MACHINE.- 

then  asked  whether  these  fundamental  properties 
were  themselves  those  of  a chemical  compound  or 
whether  they  were  to  be  reduced  to  the  action  of 
still  smaller  machines.  The  first,  answer  which 
biologists  gave  to  this  question  was  that  assimila- 
tion, growth,  and  reproduction  were  the  simple 
properties  of  a complex  chemical  compound.  This 
answer  was  certainly  incorrect.  Life  activities 
are  exhibited  by  no  chemical  compound,  but,  so 
far  as  we  know,  only  by  the  machine  called  the 
cell.  Thus  it  is  that  we  are  again  reduced  to  the 
problem  of  understanding  the  action  of  a machine. 

It  may  be  well  to  pause  here  a moment  to 
notice  that  this  position  very  greatly  increases 
the  difficulties  in  the  way  of  a solution  of  the 
life  problem.  If  the  physical  basis  of  life  had 
proved  to  be  a chemical  compound,  the  problem  of 
its  origin  would  have  been  a chemical  one.  Chemi- 
cal forces  exist  in  nature,  and  these  forces  are 
sufficient  to  explain  the  formation  of  any  kind  of 
chemical  compound.  The  problem  of  the  origin 
of  the  life  substance  would  then  have  been  simply 
to  account  for  certain  conditions  which  resulted 
in  such  chemical  combination  as  would  give  rise 
to  this  physical  basis  of  life.  But  now  that  the 
simplest  substance  manifesting  the  phenomena  of 
life  is  found  to  be  a machine,  we  can  no  longer 
find  in  chemical  forces  efficient  causes  for  its  for- 
mation. Chemical  forces  and  chemical  affinity 
can  explain  chemical  compounds  of  any  degree  of 
complexity,  but  they  cannot  explain  the  forma- 
tion of  machines.  Machines  are  the  result  of 
forces  of  an  entirely  different  nature.  Man  can 
manufacture  machines  by  taking  chemical  com- 
pounds and  putting  them  together  into  such  rela- 
tions that  their  interaction  will  give  certain  results. 


THE  CELL  AND  PROTOPLASM.  1 1 7 

Bits  of  iron  and  steel,  for  instance,  are  put  to- 
gether to  form  a locomotive,  but  the  action  of 
the  locomotive  depends,  not  upon  the  chemical 
forces  which  made  the  steel,  but  upon  the  rela- 
tion of  the  bits  of  steel  to  each  other  in  the  ma- 
chine. So  far  as  we  have  had  any  experience, 
machines  have  been  built  under  the  guidance  of 
intelligence  which  adapts  the  parts  to  each  other. 
When  therefore  we  find  that  the  simplest  life  sub- 
stance is  a machine,  we  are  forced  to  ask  what 
forces  exist  in  nature  which  can  in  a similar  way 
build  machines  by  the  adjustment  of  parts  to  each 
other.  But  this  topic  belongs  to  the  second  part 
of  our  subject,  and  must  be  for  the  present  post- 
poned. 

Reaction  against  the  Cell  Doctrine. — As  the 

knowledge  of  cells  which  we  have  outlined  was 
slowly  acquired,  the  conception  of  the  cell  passed 
through  various  modifications.  At  first  the  cell 
wall  was  looked  upon  as  the  fundamental  part, 
but  this  idea  soon  gave  place  to  the  belief  that  it 
was  the  protoplasm  that  was  alive.  Under  the  in- 
fluence of  this  thought  the  cell  doctrine  developed 
into  something  like  the  following:  The  cell  is 
simply  a bit  of  protoplasm  and  is  the  unit  of  liv- 
ing matter.  The  bodies  of  all  larger  animals  and 
plants  are  made  up  of  great  numbers  of  these 
units  acting  together,  and  the  activities  of  the 
entire  organism  are  simply  the  sum  of  the  activi- 
ties of  its  cells.  The  organism  is  thus  simply  the 
sum  of  the  cells  which  compose  it,  and  its  activi- 
ties the  sum  of  the  activities  of  the  individual 
cells.  As  more  facts  were  disclosed  the  idea 
changed  slightly.  The  importance  of  the  nucleus 
became  more  and  more  forcibly  impressed  upon 
microscopists,  and  this  body  came  after  a little 


1 1 8 THE  STORY  OF  THE  LIVING  MACHINE. 

into  such  prominence  as  to  hide  from  view  the 
more  familiar  protoplasm.  The  marvellous  activi- 
ties of  the  nucleus  soon  caused  it  to  be  regarded 
as  the  important  part  of  the  cell,  while  all  the  rest 
was  secondary.  The  cell  was  now  thought  of  as 
a bit  of  nuclear  matter  surrounded  by  secondary 
parts.  The  marvellous  activities  of  the  nucleus, 
and  above  all,  the  fact  that  the  nucleus  alone 
is  handed  down  from  one  generation  to  the  next 
in  reproduction,  all  attested  to  its  great  impor- 
tance and  to  the  secondary  importance  of  the  rest 
of  the  cell. 

This  was  the  most  extreme  position  of  the  cell 
doctrine.  The  cell  was  the  unit  of  living  action, 
and  the  higher  animal  or  plant  simply  a colony  of- 
such  units.  An  animal  was  simply  an  association 
together  for  mutual  advantage  of  independent 
units,  just  as  a city  is  an  association  of  indepen- 
dent individuals.  The  organization  of  the  animals 
was  simply  the  result  of  the  combination  of  many 
independent  units.  There  was  no  activity  of  the 
organism  as  a whole,  but  only  of  its  independent 
parts.  Cell  life  was  superior  to  organized  life. 
Just  as,  in  a city,  the  city  government  is  a name 
given  to  the  combined  action  of  the  individuals, 
so  are  the  actions  of  organisms  simply  the  com- 
bined action  of  their  individual  cells. 

Against  such  an  extreme  position  there  has 
been  in  recent  years  a decided  reaction,  and  to- 
day it  is  becoming  more  and  more  evident  that 
such  a position  cannot  be  maintained.  In  the 
first  place,  it  is  becoming  evident  that  the  cell 
substance  is  not  to  be  entirely  obliterated  by  the 
importance  of  the  nucleus.  That  the  nucleus  is 
a most  important  vital  centre  is  clear  enough,  but 
it  is  equally  clear  that  nucleus  and  cell  substance 


THE  CELL  AND  PROTOPLASM.  119 

must  be  together  to  constitute  the  life  substance. 
The  complicated  structure  of  the  cell  substance, 
the  decided  activity  shown  by  its  fibres  in  the 
process  of  cell  division,  clearly  enough  indicate 
that  it  is  a part  of  the  cell  which  can  not  be  ne- 
glected in  the  study  of  the  life  substance.  Again 
the  discovery  of  the  centrosome  as  a distinct 
morphological  element  has  still  further  added 
to  the  complexity  of  the  life  substance,  and 
proved  that  neither  nucleus  nor  cell  substance 
can  be  regarded  as  the  cell  or  as  constituting 
life.  It  is  true  that  we  may  not  yet  know  the 
source  of  this  centrosome.  We  do  not  know 
whether  it  is  handed  down  from  generation  to 
generation  like  the  nucleus,  or  whether  it  can 
be  made  anew  out  of  the  cell  substance  in  the  life 
of  an  ordinary  cell.  But  this  is  not  material  to 
its  recognition  as  an  organ  of  importance  in  the 
cell  activity.  Thus  the  cell  proves  itself  not  to 
be  a bit  of  nuclear  matter  surrounded  by  second- 
ary parts,  but  a community  of  several  perhaps 
equally  important  interrelated  members. 

Another  series  of  observations  weakened  the 
cell  doctrine  in  an  entirely  different  direction.  It 
had  been  assumed  that  the  body  of  the  multicellu- 
lar animal  or  plant  was  made  of  independent 
units.  Microscopists  of  a few  years  ago  began  to 
suggest  that  the  cells  are  in  reality  not  separated 
from  each  other,  but  are  all  connected  by  proto- 
plasmic fibres.  In  quite  a number  of  different 
kinds  of  tissue  it  has  been  determined  that  fine 
threads  of  protoplasmic  material  lead  from  one 
cell  to  another  in  such  a way  that  the  cells  are  in 
vital  connection.  The  claim  has  been  made  that 
there  is  thus  a protoplasmic  connection  between 
all  the  cells  of  the  body  of  the  animal,  and  that 
9 


120  THE  STORY  OF  THE  LIVING  MACHINE. 

thus  the  animal  or  plant,  instead  of  consisting  of 
a large  number  of  separate  independent  cells,  con- 
sists of  one  great  mass  of  living  matter  which  is 
aggregated  into  little  centres,  each  commonly  hold- 
ing a nucleus.  Such  a conclusion  is  not  yet  dem- 
onstrated, nor  is  its  significance  very  clear  should 
it  prove  to  be  a fact ; but  it  is  plain  that  such  sug- 
gestions quite  decidedly  modify  the  conception  of 
the  body  as  a community  of  independent  cells. 

There  is  yet  another  line  of  thought  which  is 
weakening  this  early  conception  of  the  cell  doc- 
trine. There  is  a growing  conviction  that  the 
view  of  the  organism,  simply  as  the  sum  of  the 
activities  of  the  individual  cells,  is  not  a correct 
understanding  of  it.  According  to  this  extreme 
position,  a living  thing  can  have  no  organization 
until  it  appears  as  the  result  of  cell  multiplica- 
tion. To  take  a concrete  case,  the  egg  of  a starfish 
can  not  possess  any  organization  corresponding 
to  the  starfish.  The  egg  is  a single  cell,  and  the 
starfish  a community  of  cells.  The  egg  can, 
therefore,  no  more  contain  the  organization  of  a 
starfish  than  a hunter  in  the  backwoods  can 
contain  within  himself  the  organization  of  a great 
metropolis.  The  descendants  of  individuals  like 
the  hunter  may  unite  to  form  a city,  and  the  de- 
scendants of  the  egg  cell  may,  by  combining,  give 
rise  to  the  starfish.  But  neither  can  the  man  con- 
tain within  himself  the  organization  of  the  city,  nor 
the  egg  that  of  the  starfish.  It  is,  perhaps,  true 
that  such  an  extreme  position  of  the  cell  doctrine 
has  not  been  held  by  any  one,  but  thoughts  very 
closely  approximating  to  this  view  have  been  held 
by  the  leading  advocates  of  the  cell  doctrine,  and 
have  beyond  question  been  the  inspiration  of  the 
development  of  that  doctrine. 


THE  CELL  AND  PROTOPLASM. 


I 2 I 


But  certainly  no  such  conception  of  the  signifi- 
cance of  cell  structure  would  longer  be  held.  In 
spite  of  the  fact  that  the  egg  is  a single  cell,  it  is 
impossible  to  avoid  the  belief  that  in  some  way  it 
contains  the  starfish.  We  need  not,  of  course, 
think  of  it  as  containing  the  structure  of  a starfish, 
but  we  are  forced  to  conclude  that  in  some  way 
its  structure  is  such  that  it  contains  the  starfish 
potentially.  The  relation  of  its  parts  and  the 
forces  therein  are  such  that,  when  placed  under 
proper  conditions,  it  develops  into  a starfish.  An- 
other egg  placed  under  identical  conditions  will 
develop  into  a sea  urchin,  and  another  into  an 
oyster.  If  these  three  eggs  have  the  power  of  de- 
veloping into  three  different  animals  under  iden- 
tical conditions,  it  is  evident  that  they  must  have 
corresponding  differences  in  spite  of  the  fact  that 
each  is  a single  cell.  Each  must  in  some  way 
contain  its  corresponding  adult.  In  other  words, 
the  organization  must  be  within  the  cells,  and 
hence  not  simply  produced  by  the  associations  of 
cells. 

Over  this  subject  there  has  been  a deal  of  puz- 
zling and  not  a little  experimentation.  The  pres- 
ence of  some  sort  of  organization  in  the  egg  is 
clear — but  what  is  meant  by  this  statement  is  not 
quite  so  clear.  Is  this  adult  organization  in  the 
whole  egg  or  only  in  its  nucleus,  and  especially  in 
the  chromosomes  which,  as  we  have  seen,  contain 
the  hereditary  traits  ? When  the  egg  begins  to 
divide  does  each  of  the  first  two  cells  still  contain 
potentially  the  organization  of  the  whole  adult, 
or  only  one  half  of  it  ? Is  the  development  of  the 
egg  simply  the  unfolding  of  some  structure  al- 
ready present;  or  is  the  structure  constantly  de- 
veloping into  more  and  more  complicated  condi- 


122  THE  STORY  OF  THE  LIVING  MACHINE. 


tions  owing  to  the  bringing  of  its  parts  into  new 
relations  ? To  answer  these  questions  experimen- 
ters have  been  engaged  in  dividing  developing 
eggs  into  pieces  to  determine  what  powers  are  still 
possessed  by  the  fragments.  The  results  of  such 
experiments  are  as  yet  rather  conflicting,  but  it 
is  evident  enough  from  them  that  we  can  no  longer 
look  upon  the  egg  cell  as  a simple  undifferentiated 
cell.  In  some  way  it  already  contains  the  charac- 
ters of  the  adult,  and  when  we  remember  that  the 
characters  of  the  adult  which  are  to  be  developed 
from  the  egg  are  already  determined,  even  to  many 
minute  details — such,  for  instance,  as  the  inherit- 
ance of  a congenital  mark — it  becomes  evident 
that  the  egg  is  a body  of  extraordinary  complexity. 
And  yet  the  egg  is  nothing  more  than  a single  cell 
agreeing  with  other  cells  in  all  its  general  charac- 
ters. It  is  clear,  then,  that  we  must  look  upon  or- 
ganization as  something  superior  to  cells  and  some- 
thing existing  within  them,  or  at  least  within  the 
egg  cell,  and  controlling  its  development.  We  are 
forced  to  believe,  further,  that  there  may  be  as  im- 
portant differences  between  two  cells  as  there  are 
between  two  adult  animals  or  plants.  In  some  way 
there  must  be  concealed  within  the  two  cells  which 
constitute  the  egg  of  the  starfish  and  the  man  dif- 
ferences which  correspond  to  the  differences  be- 
tween the  starfish  and  the  man.  Organization,  in 
other  words,  is  superior  to  cell  structure,  and  the 
cell  itself  is  an  organization  of  smaller  units. 

As  the  result  of  these  various  considerations 
there  has  been,  in  recent  years,  something  of  a re- 
action against  the  cell  doctrine  as  formerly  held. 
While  the  study  of  cells  is  still  regarded  as  the 
key  to  the  interpretation  of  life  phenomena,  biol- 
ogists are  seeing  more  and  more  clearly  that  they 


THE  CELL  AND  PROTOPLASM.  123 

must  look  deeper  than  simple  cell  structure  for 
their  explanation  of  the  life  processes.  While  the 
study  of  cells  has  thrown  an  immense  amount  of 
light  upon  life,  we  seem  hardly  nearer  the  centre 
of  the  problem  than  we  were  before  the  beginning 
of  the  series  of  discoveries  inaugurated  by  the 
formulation  of  the  doctrine  of  protoplasm. 

Fundamental  Vital  Activities  as  Located  in 
Cells. — We  are  now  in  position  to  ask  whether  our 
knowledge  of  cells  has  aided  us  in  finding  an 
explanation  of  the  fundamental  vital  actions  to 
which,  as  we  have  seen,  life  processes  are  to  be 
reduced.  The  four  properties  of  irritability,  con- 
tractibility,  assimilation,  and  reproduction,  belong 
to  these  vital  units — the  cells,  and  it  is  these  prop- 
erties which  we  are  trying  to  trace  to  their  source 
as  a foundation  of  vital  activity. 

We  may  first  ask  whether  we  have  any  facts 
which  indicate  that  any  special  parts  of  the  cell 
are  associated  with  any  of  these  fundamental  ac- 
tivities. The  first  fact  that  stands  out  clearly  is 
that  the  nucleus  is  connected  most  intimately  with 
the  process  of  reproduction  and  especially  with 
heredity.  This  has  long  been  believed,  but  has 
now  been  clearly  demonstrated  by  the  experiments 
of  cutting  into  fragments  the  cell  bodies  of  uni- 
cellular animals.  As  already  noticed,  those  pieces 
which  possess  a nucleus  are  able  to  continue  their 
life  and  reproduce  themselves,  while  those  without 
a nucleus  are  incapable  of  reproduction.  With 
greater  force  still  is  the  fact  shown  by  the  process 
of  fertilization  of  the  egg.  The  egg  is  very  large 
and  the  male  reproductive  cell  is  very  small,  and 
the  amount  of  material  which  the  offspring  de- 
rives from  its  mother  is  very  great  compared  with 
that  which  it  derives  from  its  father.  But  thq 


124  THE  STORY  OF  THE  LIVING  MACHINE. 


child  inherits  equally  from  father  and  mother,  and 
hence  we  must  find  the  hereditary  traits  handed 
down  in  some  element  which  the  offspring  obtains 
equally  from  father  and  mother.  As  we  have  seen 
(Figs.  34-44),  the  only  element  which  answers  this 
demand  is  the  nucleus,  and  more  particularly  the 
chromosomes  of  the  nucleus.  Clearly  enough, 
then,  we  must  look  upon  the  nucleus  as  the  special 
agent  in  reproduction  of  cells. 

Again,  we  have  apparently  conclusive  evidence 
that  the  nucleus  controls  that  part  of  the  assimila- 
tive process  which  we  have  spoken  of  as  the  con- 
structive processes.  The  metabolic  processes  of 
life  are  both  constructive  and  destructive.  By  the 
former,  the  material  taken  into  the  cell  in  the  form 
of  food  is  built  up  into  cell  tissue,  such  as  linin, 
microsomes,  etc.,  and,  by  the  latter,  these  products 
are  to  a greater  or  less  extent  broken  to  pieces 
again  to  liberate  their  energy,  and  thus  give  rise 
to  the  activities  of  the  cell.  If  the  destructive 
processes  were  to  go  on  alone  the  organism  might 
continue  to  manifest  its  life  activities  for  a time 
until  it  had  exhausted  the  products  stored  up.  in 
its  body  for  such  purposes,  but  it  would  die  from 
the  lack  of  more  material  for  destruction.  Life 
is  not  complete  without  both  processes.  Now,  in 
the  life  of  the  cell  we  may  apparently  attribute 
the  destructive  processes  to  the  cell  substance  and 
the  constructive  processes  to  the  nucleus.  In  a 
cell  which  has  been  cut  into  fragments  those  pieces 
without  a nucleus  continue  to  show  the  ordinary 
activities  of  life  for  a time,  but  they  do  not  live 
very  long  (Fig.  25).  The  fragment  is  unable  to 
assimilate  its  food  sufficiently  to  build  up  more 
material.  So  long  as  it  still  retains  within  itself  a 
sufficiency  of  already  formed  tissue  for  its  destruc- 


THE  CELL  AND  PROTOPLASM.  125 

tive  metabolism,  it  can  continue  to  move  around 
actively  and  behave  like  a complete  cell,  but 
eventually  it  dies  from  starvation.  On  the  other 
hand,  those  fragments  which  retain  a piece  of  the 
nucleus,  even  though  they  have  only  a small  por- 
tion of  the  cell  substance,  feed,  assimilate,  and 
grow;  in  other  words,  they  carry  on  not  only  the 
destructive  but  also  the  constructive  changes. 
Plainly,  this  means  that  the  nucleus  controls  the 
constructive  processes,  although  it  does  not  neces- 
sarily mean  that  the  cell  substance  has  no  share 
in  these  constructive  processes.  Without  the  nu- 
cleus the  cell  is  unable  to  perform  those  processes, 
while  it  is  able  to  carry  on  the  destructive  pro- 
cesses readily  enough.  The  nucleus  controls, 
though  it  may  not  entirely  carry  on,  the  construc- 
tive metabolism. 

It  is  equally  clear  that  the  cell  substance  is  the 
seat  of  most  of  the  destructive  processes  which 
constitute  vital  action.  The  cell  substance  is  irri- 
table, and  is  endowed  with  the  power  of  contrac- 
tility. Cell  fragments  without  nucleii  are  sensi- 
tive enough,  and  can  move  around  as  readily  as 
normal  cells.  Moreover,  the  various  fibres  which 
surround  the  centrosomes  in  cell  division  and  whose 
contractions  and  expansions,  as  we  have  seen, 
pull  the  chromosomes  apart  in  cell  division,  are 
parts  of  the  cell  substance.  All  of  these  are  the 
results  of  destructive  metabolism,  and  we  must, 
therefore,  conclude  that  destructive  processes  are 
seated  in  the  cell  substance. 

The  centrosome  is  too  problematical  as  yet  for 
much  comment.  It  appears  to  be  a piece  of  the 
machinery  for  bringing  about  cell  division,  but 
beyond  this  it  is  not  safe  to  make  any  statements. 

In  brief,  then,  the  cell  body  is  a machine  for 


126  THE  STORY  OF  THE  LIVING  MACHINE. 

carrying  on  destructive  chemical  changes,  and 
liberating  from  the  compounds  thus  broken  to 
pieces  their  inclosed  energy,  which  is  at  once  con- 
verted into  motion  or  heat  or  some  other  form  of 
active  energy.  This  chemical  destruction  is,  how- 
ever, possible  only  after  the  chemical  compounds 
have  become  a part  of  the  cell.  The  cell,  there- 
fore, possesses  a nucleus  which  has  the  power  of 
enabling  it  to  assimilate  its  food — that  is,  to  con- 
vert it  into  its  own  substance.  The  nucleus  further 
contains  a marvellousmaterial — chromatin — which 
in  some  way  exercises  a controlling  influence  in  its 
life  and  is  handed  down  from  one  generation  to 
another  by  continuous  descent.  Lastly,  the  cell 
has  the  centrosome,  which  brings  about  cell  divi- 
sion in  such  a manner  that  this  chromatin  mate- 
rial is  divided  equally  among  the  subsequent  de- 
scendants, and  thus  insures  that  the  daughter  cells 
shall  all  be  equivalent  to  each  other  and  to  the 
mother  cell. 

We  must  therefore  look  upon  the  organic  cell 
as  a little  engine  with  admirably  adapted  parts. 
Within  this  engine  chemical  activity  is  excited. 
The  fuel  supplied  to  the  engine  is  combined  by 
chemical  forces  with  the  oxygen  of  the  air.  The 
vigour  of  the  oxidation  is  partly  dependent  upon 
temperature,  just  as  it  is  in  any  other  oxidation 
process,  and  is  of  course  dependent  upon  the 
presence  of  fuel  to  be  oxidized,  and  air  to  furnish 
the  oxygen.  Unless  the  fuel  is  supplied  and  the 
air  has  free  access  to  it,  the  machine  stops,  the 
cell  dies.  The  energy  liberated  in  this  machine 
is  converted  into  motion  or  some  other  form. 
We  do  not  indeed  understand  the  construction  of 
the  machine  well  enough  to  explain  the  exact 
mechanism  by  which  this  conversion  takes  place, 


THE  CELL  AND  PROTOPLASM.  127 

but  that  there  is  such  a mechanism  can  not  be 
doubted,  and  the  structure  of  the  cell  is  certainly 
complex  enough  to  give  plenty  of  room  for  it. 
The  irritability  of  the  cell  is  easily  understood  ; 
for,  since  it  is  made  of  very  unstable  chemical 
compounds,  any  slight  disturbance  or  stimulation 
on  one  part  will  tend  to  upset  its  chemical  stabil- 
ity and  produce  reaction  ; and  this  is  what  is  meant 
by  irritability. 

Or,  again,  we  may  look  upon  the  cell  as  a little 
chemical  laboratory,  where  chemical  changes  are 
constantly  occurring.  These  changes  we  do  not 
indeed  understand,  but  they  are  undoubtedly 
chemical  changes.  The  result  is  that  some  com- 
pounds are  pulled  to  pieces  and  part  of  the  frag- 
ments liberated  or  excreted,  while  other  parts  are 
retained  and  built  into  other  more  complex  com- 
pounds. The  compounds  thus  manufactured  are 
retained  in  the  cell  body,  and  it  grows  in  bulk. 
This  continues  until  the  cell  becomes  too  big,  and 
then  it  divides. 

If  a machine  is  broken  it  ceases  to  carry  on 
its  proper  duties,  and  if  the  parts  are  badly  broken 
it  is  ruined.  So  with  the  cell.  If  it  is  broken  by 
any  means,  mechanical,  thermal,  or  otherwise,  it 
ceases  to  run — we  say  it  dies.  It  has  within 
itself  great  power  of  repairing  injury,  and  there- 
fore it  does  not  cease  to  act  until  the  injury  is 
so  great  as  to  be  beyond  repair.  Thus  it  only 
stops  its  motion  when  the  machinery  has  become 
so  badly  injured  as  to  be  beyond  hope  of  repair, 
and  hence  the  cell,  after  once  ceasing  its  action, 
can  never  resume  it  again. 

There  are,  of  course,  other  functions  of  living 
things  besides  the  few  simple  ones  which  we  have 
considered.  But  these  are  the  fundamental  ones; 


128  THE  STORY  OF  THE  LIVING  MACHINE. 

and  if  we  can  reduce  them  to  an  intelligible  ex- 
planation, we  may  feel  that  we  have  really  grasped 
the  essence  of  life.  If  we  understand  how  the 
cell  can  move  and  grow  and  reproduce  itself,  we 
may  rest  assured  that  the  other  phenomena  of 
life  follow  as  a natural  consequence.  If,  there- 
fore, we  have  obtained  an  understanding  of 
these  fundamental  vital  phenomena,  we  have 
accomplished  our  object  of  comprehending  the 
life  phenomena  in  our  chemical  and  mechanical 
laws. 

But  have  we  thus  reduced  these  fundamental 
phenomena  to  an  intelligible  explanation?  It 
must  be  acknowledged  that  we  have  not.  We 
have  reduced  them  to  the  action  of  chemical 
forces  acting  in  a machine.  But  the  machine 
itself  is  unintelligible.  The  organic  cell  is  no 
more  intelligible  to  u.s  than  is  the  body  as  a 
whole.  The  chemical  understanding  which  we 
thought  we  had  a few  years  ago  in  protoplasm 
has  failed  us,  and  nothing  has  taken  its  place 
We  have  no  conception  of  what  may  be  the  prim- 
itive life  substance.  All  we  can  say  is  that  this 
most  marvellous  of  all  natural  phenomena  occurs 
only  within  that  peculiar  piece  of  machinery 
which  we  call  the  cell,  and  that  it  is  the  result  of 
the  action  of  physical  forces  in  that  machine. 
How  the  machine  acts,  or  even  the  structure  of 
the  machine,  we  are  as  far  from  understanding  as 
we  were  fifty  years  ago.  The  solution  has  re- 
treated before  us  even  faster  than  we  have  ad- 
vanced toward  it. 

Summary. — We  may  now  notice  in  a brief  sum- 
mary the  position  which  we  have  reached.  In 
our  attempt  to  explain  the  living  organism  on  the 
principle  of  the  machine,  we  are  very  successful 


THE  CELL  AND  PROTOPLASM.  1 29 

so  far  as  secondary  problems  are  concerned.  Di- 
gestion, circulation,  respiration,  and  motion  are 
readily  solved  upon  chemical  and  mechanical 
principles.  Even  the  phenomena  of  the  nervous 
system  are,  in  a measure,  capable  of  comprehen- 
sion within  a mechanical  formula,  leaving  out  of 
account  the  purely  mental  phenomena  which  cer- 
tainly have  not  been  touched  by  the  investi- 
gation. All  of  these  phenomena  are  reducible  to 
a few  simple  fundamental  activities,  and  these 
fundamental  activities  we  find  manifested  by 
simple  bits  of  living  matter  unincumbered  by  the 
complicated  machinery  of  organisms.  With  the 
few  fundamental  properties  of  these  bits  of  or- 
ganic matter  we  can  construct  the  complicated 
life  of  the  higher  organism.  When  we  come, 
however,  to  study  these  simple  bits  of  matter,  they 
prove  to  be  anything  but  simple  bits  of  matter. 
They,  too,  are  pieces  of  complicated  mechanism 
whose  action  we  do  not  even  hope  to  understand. 
That  their  action  is  dependent  upon  their  ma- 
chinery is  evident  enough  from  the  simple  de- 
scription of  cell  activity  which  we  have  noticed. 
That  these  fundamental  vital  properties  are  to  be 
explained  as  the  result  of  chemical  and  mechan- 
ical forces  acting  through  this  machinery,  can  not 
be  doubted.  But  how  this  occurs  or  what  consti- 
tutes the  guiding  force  which  corresponds  to  the 
engineer  of  the  machine,  we  do  not  know. 

Thus  our  mechanical  explanation  of  the  living 
machine  lacks  a foundation.  We  can  understand 
tolerably  well  the  building  of  the  superstructure, 
but  the  foundation  stones  upon  which  that  struc- 
ture is  built  are  unintelligible  to  us.  The  run- 
ning of  the  living  machine  is  thus  only  in  part 
understood.  The  living  organism  is  a machine 


130  THE  STORY  OF  THE  LIVING  MACHINE. 

or,  it  is  better  to  say,  it  is  a series  of  machines  one 
within  the  other.  As  a whole  it  is  a machine,  and 
its  parts  are  separate  machines.  Each  part  is 
further  made  up  of  still  smaller  machines  until  we 
reach  the  realm  of  the  microscope.  Here  still  we 
find  the  same  story.  Even  the  parts  formerly 
called  units,  prove  to  be  machines,  and  when  we 
recognize  the  complexity  of  these  cells  and  their 
marvellous  activities,  we  are  ready  to  believe  that 
we  may  find  still  further  machines  within.  And 
thus  vital  activity  is  reduced  to  a complex  of  ma- 
chines, all  acting  in  harmony  with  each  other  to 
produce  together  the  one  result — life. 


PART  II. 


THE  BUILDING  OF  THE  LIVING 
MACHINE. 


CHAPTER  III. 

THE  FACTORS  CONCERNED  IN  THE  BUILDING  OF 
THE  LIVING  MACHINE. 

Having  now  outlined  the  results  of  our  study 
into  the  mechanism  of  the  living  machine,  we  turn 
our  attention  next  to  the  more  difficult  problem 
of  the  method  by  which  this  machine  was  built. 
From  the  facts  which  we  have  been  considering 
in  the  last  two  chapters  it  is  evident  that  the 
problem  we  have  before  us  is  a mechanical  rather 
than  a chemical  one.  Of  course,  chemical  forces 
lie  at  the  bottom  of  vital  activity,  and  we  must 
look  upon  the  force  of  chemical  affinity  as  the 
fundamental  power  to  which  the  problems  must  be 
referred.  But  a chemical  explanation  will  evident- 
ly not  suffice  for  our  purpose  ; for  we  have  abso- 
lutely no  reason  for  believing  that  the  phenomena 
of  life  can  occur  as  the  results  of  the  chemical 
properties  of  any  compound,  however  complex. 
The  simplest  known  form  of  matter  which  manifests 
life  is  a machine,  and  the  problem  of  the  origin  of 
life  must  be  of  the  origin  of  that  machine.  Are 

131 


132  THE  STORY  OF  THE  LIVING  MACHINE. 

there  any  forces  in  nature  which  are  of  a sort  as 
to  enable  us  to  use  them  to  explain  the  building 
of  machines?  Plants  and  animals  are  the  only 
machines  which  nature  has  produced.  They  are 
the  only  instances  in  nature  of  a structure  built 
with  its  parts  harmoniously  adjusted  to  each  other 
to  the  performance  of  certain  ends.  All  other 
machines  with  which  we  are  acquainted  were 
made  by  man,  and  in  making  them  intelligence 
came  in  to  adapt  the  parts  to  each  other.  But  in 
the  living  organism  is  a similarly  adapted  ma  • 
chine  made  by  natural  means  rather  than  arti- 
ficial. How  were  they  built  ? Does  nature,  apart 
from  human  intelligence,  possess  forces  which  can 
achieve  such  results? 

Here  again  we  must  attack  the  problem  from 
what  seems  to  be  the  wrong  end.  Apparently  it 
would  be  simpler  to  discover  the  method  of  the 
manufacture  of  the  simplest  machine  rather  than 
the  more  complex  ones.  But  this  has  proved  con- 
trary to  the  fact.  Perhaps  the  chief  reason  is  that 
the  simplest  living  machine  is  the  cell  whose  study 
must  always  involve  the  use  of  the  microscope, 
and  for  this  reason  is  more  difficult.  Perhaps  it  is 
because  the  problem  is  really  a more  difficult  one 
than  to  explain  the  building  of  the  more  complex 
machines  out  of  the  simpler  ones.  At  all  events, 
the  last  fifty  years  have  told  us  much  of  the 
method  of  the  building  of  the  complex  machines 
out  of  the  simpler  ones,  while  we  have  as  yet  not 
even  a hint  as  to  the  solution  of  the  building  of 
the  simplest  machine  from  the  inanimate  world. 
Our  attention  must,  therefore,  be  first  directed  to 
the  method  by  which  nature  has  constructed  the 
complex  machines  which  we  find  filling  the  world 
to-day  in  the  form  of  animals  and  plants. 


THE  LIVING  MACHINE  BUILDING  FACTORS.  133 

History  of  the  Living  Machine. — In  the  first 
place,  we  must  notice  that  these  machines  have 
not  been  fashioned  suddenly  or  rapidly,  but  have 
been  the  result  of  a very  slow  growth.  They 
have  had  a history  extending  very  far  back  into 
the  past  for  a period  of  years  which  we  can  only 
indefinitely  estimate,  but  certainly  reaching  into 
the  millions.  As  we  look  over  this  past  history 
in  the  light  of  our  present  knowledge  we  see  that 
whatever  have  been  the  forces  which  have  been 
concerned  in  the  construction  of  these  machines 
they  have  acted  very  slowly.  It  has  taken  cen- 
turies, and,  indeed,  thousands  of  years,  to  take  the 
successive  steps  which  have  been  necessary  in  this 
construction.  Secondly,  we  notice  that  the  ma- 
chines have  been  built  up  step  by  step,  one  fea- 
ture being  added  to  another  with  the  slowly  pro- 
gressing ages.  Thirdly,  we  notice  that  in  one 
respect  this  construction  of  the  living  machine 
by  nature’s  processes  has  been  different  from 
our  ordinary  method  of  building  machines.  Our 
method  of  building  puts  the  parts  gradually  into 
place  in  such  a way  that  until  the  machine  is  fin- 
ished it  is  incapable  of  performing  its  functions. 
The  half-built  engine  is  as  useless  and  as  power- 
less as  so  much  crude  iron.  Its  power  of  action 
only  appears  after  the  last  part  is  fitted  into  place 
and  the  machine  finished.  But  nature’s  process 
in  machine  building  is  different.  Every  step  in 
the  process,  so  far  as  we  can  trace  it  at  least, 
has  produced  a complete  machine.  So  far  back 
as  we  can  follow  this  history  we  find  that  at 
every  point  the  machine  was  so  complete  as  to 
be  always  endowed  with  motion  and  life  activity. 
Nature’s  method  has  been  to  take  simpler  types 
of  machines  and  slowly  change  them  into  more 


134  the  story  of  the  living  machine. 

complicated  ones  without  at  any  moment  impair- 
ing their  vigour.  It  is  something  as  if  the  steam 
engine  of  Watt  should  be  slowly  changed  by  add- 
ing piece  after  piece  until  there  was  finally  pro- 
duced the  modern  quadruple  expansion  engine, 
but  all  this  change  being  made  upon  the  original 
engine  without  once  stopping  its  motion. 

This  gradual  construction  of  the  living  ma- 
chines has  been  called  Organic  Evolution , or  the 
IVieory  of  Descent.  It  will  be  necessary  for  us,  in 
order  to  comprehend  the  problem  which  we  have 
before  us,  to  briefly  outline  the  course  of  this  evo- 
lution. Our  starting  point  in  this  history  must 
be  the  cell,  for  such  is  the  earliest  and  simplest 
form  of  living  thing  of  which  we  have  any  trace. 
This  cell  is,  of  course,  already  a machine,  and  we 
must  presently  return  to  the  problem  of  its  origin. 
At  present  we  will  assume  this  cell  as  a starting  * 
point  endowed  with  its  fundamental  vital  powers. 
It  was  sensitive,  it  could  feel,  grow,  and  repro- 
duce itself.  From  such  a simple  machine,  thus 
endowed,  the  history  has  been  something  as  fol- 
lows: In  reproducing  itself  this  machine,  as  we 
have  already  seen,  simply  divided  itself  into  two 
halves,  each  like  the  other.  At  first  all  the  parts 
thus  arising  separated  from  each  other  and  re- 
mained independent.  But  so  long  as  this  habit 
continued  there  could  be  little  advance.  After  a 
time  some  of  the  cells  failed  to  separate  after 
division,  but  remained  clinging  together  (Fig.  45). 
The  cells  of  such  a mass  must  have  been  at  first 
all  alike;  but,  after  a little,  differences  began  to 
appear  among  them.  Those  on  the  outside  of  the 
mass  were  differently  affected  by  their  surround- 
ings from  those  in  the  interior,  and  soon  the  cells 
began  to  share  among  themselves  the  different 


THE  LIVING  MACHINE  BUILDING  FACTORS.  135 

duties  of  life.  The  cells  on  the  outside  were  bet- 
ter situated  for  protection  and  capturing  food, 
while  those  on  the  inside  could  not  readily  seize 
food  for  themselves,  and  took  upon 
themselves  the  duty  of  digesting  the 
food  which  was  handed  to  them  by 
the  outer  cells.  Each  of  these  sets 
of  cells  could  now  carry  on  its  own 
special  duties  to  better  advantage, 
since  it  was  freed  from  other  duties,  A ^ig.  45- 
and  thus  the  whole  mass  of  cells  resulting  from 
was  better  served  than  when  each  division,  repre- 
cell  tried  to  do  everything  for  itself.  stepTnmachine 
This  was  the  first  step  in  the  build-  making, 
ing  of  the  machine  out  of  the  active 
cells  (Fig.  46).  From  such  a starting  point  the  sub' 
seqaent  history  has  been  ever  based  upon  the  same 
principle.  There  has  been  a con^ 
stant  separation  of  the  different 
functions  of  life  among  groups 
of  cells,  and  as  the  history  went 
on  this  division'  of  labor  among 
the  different  parts  became 
greater  and  greater.  Group 
after  group  of  cells  were  set 
apart  for  one  special  duty  after 
another,  and  the  result  was  a 
larger  and  ever  more  complicat- 
ed mass  of  cells,  with  a greater 
and  greater  differentiation 
among  them.  In  this  building 
of  the  machine  there  was  no 
time  when  the  machine  was  not 
active.  At  all  points  the  ma- 
chine was  alive  and  functional,  but  each  step  made 
the  total  function  of  the  machine  a little  more 


Fig.  46. 

A later  step  in  machine 
building  in  which 
the  outer  cells  have 
acquired  different 
form  and  function 
from  the  inner  cells : 
ec,  the  outer  cells, 
whose  duties  are 
protective ; en,  the 
inner  cells  engaged 
in  digesting  food. 


IO 


136  THE  STORY  OF  THE  LIVING  MACHINE. 

accurately  performed,  and  hence  raised  somewhat 
the  totality  of  life  powers.  This  parcelling  out  of 
the  different  duties  of  life  to  groups  of  cells  con- 
tinued age  after  age,  each  step  being  a little  ad- 
vance over  the  last,  until  the  result  has  been  the 
living  machine  as  we  know  it  in  its  highest  form, 
with  its  numerous  organs,  all  interrelated  in  such 
a way  as  to  form  a harmoniously  acting  whole. 

But  a second  principle  in  this  growth  of  the 
machine  was  needed  to  produce  the  variety  which 
is  found  in  nature.  As  the  different  cells  in  the 
multicellular  mass  became  associated  into  groups 
for  different  duties,  the  method  of  such  division  of 
labor  was  not  alike  in  all  machines.  A city  in 
China  and  one  in  America  are  alike  made  up  of 
individuals,  and  the  fundamental  needs  of  the 
Chinaman  and  the  American  are  alike.  But  dif- 
ferences in  industrial  and  political  conditions 
have  produced  different  combinations  and  asso- 
ciations, so  that  Pekin  is  wonderfully  unlike  New 
York.  So  in  these  early  developing  machines, 
quite  a variety  of  method  of  organization  was 
adopted  by  the  different  groups.  Now  as  soon 
as  any  special  type  of  organization  was  adopted 
by  any  animal  or  plant,  the  principle  of  heredity 
transmitted  the  same  kind  of  organization  to'  its 
descendants,  and  there  thus  arose  lines  of  descent 
differing  from  each  other,  each  line  having  its 
own  method  of  organization.  As  we  follow  the 
history  of  each  line  the  same  thing  is  repeated. 
We  find  that  the  representatives  of  each  line 
again  separate  into  groups,  each  of  which  has  ac- 
quired some  new  type  of  organization,  and  there 
has  thus  been  a constant  divergence  of  these  lines 
of  descent  in  an  indefinite  number  of  directions. 
The  members  of  the  different  lines  of  descent  all 


THE  LIVING  MACHINE  BUILDING  FACTORS.  137 

show  a fundamental  likeness  with  each  other 
since  they  retain  the  fundamental  characters  of 
their  common  ancestor,  but  they  show  also  the 
differences  which  they  have  themselves  acquired. 
And  thus  the  process  is  repeated  over  and  over 
again.  This  history  of  the  growth  of  these  dif- 
ferent machines  has  thus  been  one  of  divergence 
from  common  centres,  and  is  to  be  diagrammati- 
cally  expressed  after  the  fashion  of  a branching 
tree.  The  end  of  each  branch  represents  the 
highest  state  of  perfection  to  which  each  line  has 
been  carried. 

One  other  point  in  this  history  must  be  noted. 
As  the  development  of  the  complication  of  the 
machine  progressed  the  possibility  of  further 
progress  has  been  constantly  narrowed.  When 
the  history  of  these  machines  began  as  a simple 
mass  of  cells,  there  was  a possibility  of  an  almost 
endless  variety  of  methods  of  organization.  But 
as  a distinct  type  of  organization  was  adopted  by 
one  and  another  line  of  descendants  all  subse- 
quent productions  were  limited  through  the  law 
of  heredity  to  the  general  line  of  organization 
adopted  by  their  ancestors.  With  each  age  the 
further  growth  of  such  machines  must  consist  in 
the  further  development  in  the  perfection  of  its 
parts,  and  not  in  the  adoption  of  any  new  system 
of  organization.  Hence  it  is  that  the  history  of 
the  living  machine  has  shown  a tendency  toward 
development  along  a few  well-marked  lines,  and 
although  this  complication  becomes  greater,  we 
still  see  the  same  fundamental  scheme  of  organi- 
zation running  through  the  whole.  As  the  ages 
have  progressed  the  machines  have  become  more 
perfect  in  the  adjustment  of  their  parts,  i.  e.,  they 
have  become  more  perfect  machines,  but  the  his- 


138  THE  STORY  OF  THE  LIVING  MACHINE. 

tory  has  been  simply  that  of  perfecting  the  early 
machines  rather  than  the  production  of  new  types. 

Evidence  for  this  History. — As  just  outlined,  we 
see  that  the  living  machines  have  been  gradually 
brought  into  their  present  condition  by  a process 
which  has  been  called  organic  evolution.  But  we 
must  pause  for  a moment  to  ask  what  is  our  evi- 
dence that  such  has  been  the  history  of  the  living 
machine.  The  whole  possibility  of  understand- 
ing living  nature  depends  upon  our  accepting 
this  history  and  finding  an  explanation  of  it.  At 
the  outset  we  have  the  question  of  fact,  and  we 
must  notice  the  grounds  upon  which  we  stand  in 
assuming  this  history  to  be  as  outlined. 

This  problem  is  the  one  which  has  occupied 
such  a prominent  place  in  the  scientific  world 
during  the  last  forty  years,  and  which  has  contrib- 
uted so  largely  toward  making  modern  biology 
such  a different  subject  from  the  earlier  studies 
of  natural  history.  It  is  simply  the  evidence 
for  organic  evolution,  or  the  theory  of  descent. 
The  subject  has  for  forty  years  been  thoroughly 
sifted  and  tested  by  every  conceivable  sort  of  test. 
As  a result  of  the  interest  in  the  question  there 
has  been  disclosed  an  immense  mass  of  evidence, 
relevant  and  irrelevant.  As  the  evidence  has  ac- 
cumulated it  has  become  more  and  more  evident 
that  the  evolution  theory  must  be  recognized  as 
the  only  one  which  is  in  accord  with  the  facts,  and 
the  outcome  has  been  a practical  unanimity  among 
thinkers  that  the  theory  of  descent  must  be  the 
foundation  of  our  further  study.  The  evidence 
which  has  forced  this  conclusion  upon  scientists 
we  must  stop  for  a moment  to  consider,  since 
it  bears  very  directly  upon  the  subject  we  are 
studying. 


THE  LIVING  MACHINE  BUILDING  FACTORS.  1 39 

Historical. — The  first  source  of  evidence  is 
naturally  a historical  one.  This  long  history  of  the 
construction  of  the  living  machine  has  left  its  rec- 
ord in  the  rocks  which  form  the  earth’s  surface. 
During  this  long  period  the  rocks  of  the  earth’s 
crust  have  been  deposited,  and  in  these  rocks  have 
been  left  samples  of  many  of  the  steps  in  this  his- 
tory of  machine  building.  The  history  can  be 
traced  by  the  study  of  these  samples  just  as  the  his- 
tory of  any  machine  might  be  traced  from  a study 
of  the  models  in  a patent  office.  One  might  very 
easily  trace,  with  most  strict  accuracy  and  minute 
detail,  the  history  of  the  printing  machine  from 
the  models  which  are  preserved  in  the  patent 
offices  and  elsewhere.  So  is  it  with  the  history  of 
the  living  machine.  To  be  sure,  the  history  is 
rather  incomplete  and  at  times  difficult  to  read. 
Many  a period  in  the  development  has  left  no 
samples  for  our  inspection  and  must  be  inter- 
preted in  our  history  between  what  went  before 
and  what  comes  after.  Many  of  the  machines, 
especially  the  early  ones,  were  made  of  such  frag- 
ile material  that  they  could  not  be  preserved  in 
the  rocks.  In  many  a case,  too,  the  rocks  in  which 
the  specimens  were  deposited  have  been  subjected 
to  such  a variety  of  heatings  and  pressures,  that 
they  have  been  twisted  out  of  shape  and  even 
crushed  out  of  recognizable  form.  But  in  spite  of 
this  the  record  is  showing  itself  more  complete 
each  year.  Our  paleontologists  are  opening  layer 
after  layer  of  these  rocks,  and  thus  examining  each 
year  new  pages  in  nature’s  history.  The  more 
recent  epochs  in  the  history  have  been  already 
read  with  almost  historic  accuracy.  From  them 
we  have  learned  in  great  detail  how  the  finishing 
touches  were  given  to  these  machines,  and  are 


140  THE  STORY  OF  THE  LIVING  MACHINE, 

able  to  trace  with  accuracy  how  the  somewhat 
more  generalized  forms  of  earlier  days  were 
changed  to  produce  our  modern  animals. 

This  fossil  record  has  given  us  our  best  knowl- 
edge of  the  course  by  which  the  present  living 
world  has  been  brought  into  its  existing  condi- 
tion. But  its  accuracy  is  largely  confined  to  the 
recent  periods.  Of  the  very  early  history  fossils 
tell  us  little  or  nothing.  All  the  early  rocks,  which 
we  may  believe  were  formed  during  the  period 
when  the  first  steps  in  this  machine  building 
were  taken,  have  been  so  changed  by  heat  and 
pressure  that  whatever  specimens  they  may  have 
originally  contained  have  been  crushed  out  of 
shape.  Furthermore,  the  earliest  organisms  had 
no  hard  skeletons,  and  it  was  not  until  living  be- 
ings had  developed  far  enough  to  have  hard  parts 
that  it  was  possible  for  them  to  leave  traces  of 
themselves  in  the  rocks.  Hence,  so  far  as  con- 
cerns this  earliest  history,  we  can  get  no  record  of 
it  in  the  rocks. 

Embryological. — But  here  comes  in  another 
source  of  evidence  which  helps  to  fill  up  the  gap. 
In  its  development  every  animal  to-day  begins  as 
an  egg.  This  is  a simple  cell,  and  the  animal  goes 
through  a series  of  changes  which  eventually  lead 
to  the  adult.  Now  these  changes  appear  for  the 
most  part  to  be  parallel  to  the  changes  through 
which  the  earlier  forms  of  life  passed  in  their 
development  from  the  simple  to  the  more  compli- 
cated forms.  Where  it  is  possible  to  follow  the 
history  of  the  groups  of  animals  from  their  fos- 
sil remains  and  compare  it  with  the  history  of 
the  individual  animal  as  it  progresses  from  the 
egg  to  the  adult,  there  is  found  a very  decided 
parallelism.  This  parallelism  between  embryology 


THE  LIVING  MACHINE  BUILDING  FACTORS.  14 1 

and  past  history  has  been  of  great  service  in 
helping  us  toward  the  history  of  the  past.  At 
one  time  it  was  believed  that  it  was  the  key 
which  would  unlock  all  doors,  and  for  a decade 
biologists  eagerly  pursued  embryology  with  the 
expectation  that  it  would  solve  all  problems  in 
connection  with  the  history  of  animals.  The 
result  has  been  somewhat  disappointing.  Embry- 
ology has,  it  is  true,  been  of  the  utmost  service  in 
showing  relationships  of  forms  to  each  other,  and 
in  thus  revealing  past  history.  But  while  this 
record  is  a valuable  one,  it  is  a record  which  has 
unfortunately  been  subject  to  such  modifying 
conditions  that  in  many  cases  its  original  mean- 
ing has  been  entirely  obliterated  and  it  has  become 
worthless  as  a historical  record.  These  imper- 
fections in  regard  to  the  record  were  early  seen 
after  the  attention  of  biologists  was  seriously 
turned  to  the  study  of  embryology,  but  it  was  ex- 
pected that  it  would  be  possible  to  correct  them 
and  discover  the  true  meaning  underlying  the 
more  apparent  one.  Indeed,  in  > many  cases  this 
has  been  found  possible.  But  many  of  the  modi- 
fications are  so  profound  as  to  render  it  impos- 
sible to  untangle  them  and  discover  the  true 
meaning.  As  a result  the  biologist  to-day  is  show- 
ing less  confidence  in  embryology,  and  is  turning 
his  attention  in  different  directions  as  more  promis- 
ing of  results  in  the  line  desired. 

But  although  the  teachings  of  embryology 
have  failed  to  realize  the  great  hopes  that  were 
placed  upon  them,  their  assistance  in  the  formula- 
tion of  this  history  of  the  machine  has  been  of 
extreme  value.  Many  a bit  of  obscurity  has  been 
cleared  up  when  the  embryology  of  puzzling  ani- 
mals has  been  studied.  Many  a relationship  has 


142  THE  STORY  OF  THE  LIVING  MACHINE. 

been  made  clear,  and  this  is  simply  another  way  of 
saying  that  a portion  of  this  history  of  life  has 
been  read.  This  aid  of  embryology  has  been  par- 
ticularly valuable  in  just  that  part  of  the  history 
where  the  evidence  from  the  study  of  fossils  is 
wanting.  The  study  of  fossils,  as  we  have  seen, 
gives  little  or  no  data  concerning  the  early  his- 
tory of  living  machines;  and  it  is  just  here  that 
embryology  has  proved  to  be  of  the  most  value. 
It  is  a source  of  evidence  that  has  told  us  of  most 
of  the  steps  in  the  progress  from  the  single-celled 
animal  to  the  multicellular  organisms,  and  gives 
us  the  clearest  idea  of  the  fundamental  principles 
which  have  been  concerned  in  the  evolution  of 
life  and  the  construction  of  the  complicated 
machine  out  of  the  simple  bit  of  protoplasm.  In 
spite  of  its  limits,  therefore,  embryology  has  con- 
tributed a large  quota  of  the  evidence  which  we 
have  of  the  evolution  of  life. 

Anatomical. — A third  source  of  this  history  is 
obtained  from  the  facts  of  comparative  anatomy. 
The  essential  feature  of  this  subject  is  the  fact  that 
animals  and  plants  show  relationships.  This  fact 
is  one  of  the  most  patent  and  yet  one  of  the  most 
suggesti  ve  facts  of  biology.  It  has  been  recognized 
from  the  very  beginning  of  the  study  of  animals 
and  plants.  One  cannot  be  even  the  most  super- 
ficial observer  without  seeing  that  certain  forms 
show  great  likeness  to  each  other  while  others  are 
much  more  unlike.  The  groupingof  animals  and 
plants  into  orders,  genera,  and  species  is  depen- 
dent upon  this  relationship.  If  two  forms  are  alike 
in  everything  except  some  slight  detail,  they  are 
commonly  placed  in  the  same  genus  but  in  differ- 
ent species,  while  if  they  show  a greater  unlike- 
ness they  may  be  placed  in  separate  genera.  By 


THE  LIVING  MACHINE  BUILDING  FACTORS.  143 

thus  grouping  together  forms  according  to  their 
resemblance  the  animal  and  vegetable  kingdoms 
are  classified  into  groups  subordinate  to  groups. 
The  principle  of  relationship,  i.  e.,  fundamental 
similarity  of  structure,  runs  through  the  whole 
animal  and  vegetable  kingdom.  Even  the  ani- 
mals most  unlike  each  other  show  certain  points 
of  similarity  which  indicates  a relationship,  al- 
though of  course  a distant  one. 

The  fact  of  such  a relationship  is  too  patent 
to  demand  more  words,  but  its  significance  needs 
to  be  pointed  out.  When  we  speak  of  relation- 
ship among  men  we  always  mean  historical  con- 
nection. Two  brothers  are  closely  related  be- 
cause they  have  sprung  from  common  parents, 
while  two  cousins  are  less  closely  related  because 
their  common  point  of  origin  was  farther  back  in 
time.  More  widely  we  speak  of  the  relationship 
of  the  Indo-European  races,  meaning  thereby 
that  back  in  the  history  of  man  these  races  had  a 
common  point  of  origin.  We  never  speak  of  any 
real  relation  of  objects  unless  thereby  we  mean  to 
imply  historical  connection.  We  are  therefore 
justified  in  interpreting  the  manifest  relationships 
of  organisms  as  pointing  to  history.  Particularly 
are  we  justified  in  this  conclusion  when  we  find 
that  the  relationships  which  we  draw  between  the 
types  of  life  now  in  existence  run  parallel  to  the 
history  of  these  types  as  revealed  to  us  by  fossils 
and  at  the  same  time  disclosed  by  the  study  of 
embryology. 

This  subject  of  comparative  anatomy  includes 
a consideration  of  what  is  called  homology,  and 
perhaps  a concrete  example  may  be  instructive 
both  in  illustration  and  as  suggesting  the  course 
which  nature  adopts  in  constructing  her  machines. 


144  THE  STORY  OF  THE  LIVING  MACHINE. 

We  speak  of  a monkey’s  arm  and  a bird’s  wing  as 
homologous,  although  they  are  wonderfully  dif- 
ferent in  appearance  and  adapted  to  different 
duties.  They  are  called  homologous  because  they 
have  similar  parts  in  similar  rela- 


Fig.  47. — The  arm  of  a monkey,  a prehensile  appendage. 

Fig.  48. — The  arm  of  a bird,  a flying  appendage.  In  life  covered 
with  feathers. 

Fig.  49. — The  arm  of  an  ancient  half-bird  half-reptile  animal.  In 
life  covered  with  feathers  and  serving  as  a wing. 

and  48,  where  it  will  be  seen  that  each  has  the 
same  bones,  although  in  the  bird’s  wing  some 
of  the  bones  have  been  fused  together  and  oth- 
ers lost.  Their  similarity  points  to  a relation- 
ship, but  their  dissimilarity  tells  us  that  the  re- 
lationship is  a distant  one,  and  that  their  com- 
mon point  of  origin  must  have  been  quite  far 
back  in  history.  Now  if  we  follow  back  the  his- 
tory of  these  two  kinds  of  appendages,  as  shown 
to  us  by  fossils,  we  find  them  approaching  a com- 
mon point,  The  arm  can  readily  be  traced  to  a 


THE  LIVING  MACHINE  BUILDING  FACTORS.  145 

walking  appendage,  while  the  bird’s  wing,  by 
means  of  some  interesting  connecting  links,  can 
in  a similar  way  be  traced  to  an  appendage  with 
its  five  fingers  all  free  and  used  for  walking. 
Fig.  49  shows  one  of  these  connecting  links  repre- 
senting the  earliest  type  of  bird,  where  the  fingers 
and  bones  of  the  arm  were  still  distinct,  and  yet 
the  whole  formed  a true  wing.  Thus  we  see  that 
the  common  point  of  origin  which  is  suggested  by 
the  likenesses  between  an  arm  and  a wing  is  no 
mere  imaginary  one,  for  the  fossil  record  has 
shown  us  the  path  leading  to  that  point  of  origin. 
The  whole  tells  us  further  that  nature’s  method 
of  producing  a grasping  or  flying  organ  was  here, 
not  to  build  a new  organ,  but  to  take  one  that  had 
hitherto  been  used  for.other  purposes,  and  by  slow 
changes  modify  its  form  and  function  until  it  was 
adapted  to  new  duties. 

Significance  of  these  Sources  of  History. — The 

real  force  of  these  sources  of  evidence  comes 
to  us  only  when  we  compare  them  with  each 
other.  They  agree  in  a most  remarkable  fash- 
ion. The  history  as  disclosed  by  fossils  and 
that  told  by  embryology  agree  with  each  other, 
and  these  are  in  close  harmony  with  the  history 
as  it  can  be  read  from  comparative  anatomy.  If 
archaeologists  were  to  find  in  different  countries 
and  entirely  unconnected  with  each  other  two  or 
more  different  records  of  a lost  nation,  the  belief 
in  the  actual  existence  of  that  nation  would  be 
irresistible.  When  researches  at  Nineveh,  for  ex- 
ample, unearth  tablets  which  give  the  history  of 
ancient  nations,  and  when  it  proves  that  among 
the  nations  thus  mentioned  are  some  with  the 
same  names  and  having  the  same  facts  of  history 
as  those  mentioned  in  the  Bible,  it  is  absolutely 


146  THE  STORY  OF  THE  LIVING  MACHINE. 

impossible  to  avoid  the  conclusion  that  such  a 
nation  with  such  a history  did  actually  exist. 
Two  independent  sources  of  record  could  not  be 
false  in  regard  to  such  a matter  as  this. 

Now,  our  sources  of  evidence  for  this  history 
of  the  living  machine  prove  to  be  of  exactly  this 
kind.  We  have  three  independent  sources  of 
evidence  which  are  so  entirely  different  from 
each  other  that  there  is  almost  no  likeness  be- 
tween them.  One  is  written  in  the  rocks,  one  in 
bone  and  muscle,  while  the  third  is  recorded  in 
the  evanescent  and  changing  pages  of  embry- 
ology and  metamorphosis.  Yet  each  tells  the 
same  story.  Each  tells  of  a history  of  this  ma- 
chine from  simple  forms  to  more  complex.  Each 
tells  of  its  greater  and  greater  differentiation  of 
labour  and  structure  as  the  periods  of  time  passed. 
Each  tells  of  a growing  complexity  and  an  in- 
creasing perfection  of  the  organisms  as  successive 
periods  pass.  Each  tells  us  of  common  points  of 
origin  and  divergence  from  these  points.  Each 
tells  us  how  the  more  complicated  forms  have 
arisen  as  the  results  of  changes  in  and  modifi- 
cations of  the  simpler  forms.  Each  shows  us 
how  the  individual  parts  of  the  organisms  have 
been  enlarged  or  diminished  or  changed  in  shape 
to  adapt  them  to  new  duties.  Each,  in  short,  tells 
the  same  story  of  the  gradual  construction  of  the 
living  machine  by  slow  steps  and  through  long 
ages  of  time.  When  these  three  sources  of  his- 
tory so  accurately  agree  with  each  other,  it  is  as 
impossible  to  disbelieve  in  the  existence  of  such 
history  as  it  is  to  disbelieve  in  the  existence  of 
the  ancient  Hittite  nation,  after  its  history  has 
been  told  to  us  by  two  different  sources  of  record. 

Now  all  this  is  very  germane  to  our  subject. 


THE  LIVING  MACHINE  BUILDING  FACTORS.  147 

We  are  trying  to  learn  how  this  living  machine, 
with  its  wonderful  capabilities,  was  built.  The 
history  which  we  have  outlined  is  undoubtedly 
the  history  of  the  building  of  this  machine,  and 
the  knowledge  that  these  complicated  machines 
have  been  produced  as  the  result  of  slow  growth 
is  of  the  utmost  importance  to  us.  This  knowl- 
edge gives  us  at  the  very  start  some  idea  of  the 
nature  of  the  forces  which  have  been  at  work.  It 
tells  us  that  in  searching  for  these  forces  we  must 
look  for  those  which  have  been  acting  constantly. 
We  must  look  for  forces  which  produce  their 
effects  not  by  sudden  additions  to  the  complica- 
tion of  the  machine.  They  must  be  constant 
forces  whose  effect  at  any  one  time  is  com- 
paratively slight,  but  whose  total  effect  is  to  in- 
crease the  complexity  of  the  machine.  They 
must  be  forces  which  produce  new  types  through 
the  modification  of  the  old  ones.  We  must  look 
for  forces  which  do  not  adapt  the  machine  for  its 
future,  but  only  for  its  present  need.  Each  step 
in  the  history  has  been  a complete  animal  with  its 
own  fully  developed  powers.  We  are  not  to  ex- 
pect to  find  forces  which  planned  the  perfect 
machine  from  the  start,  nor  forces  which  were 
engaged  in  constructing  parts  for  future  use. 
Each  step  in  the  building  of  the  machine  was 
taken  for  the  good  of  the  machine  at  the  particu- 
lar moment,  and  the  forces  which  we  are  to  look 
for  must  therefore  be  only  such  as  can  adapt  the 
organisms  for  its  present  needs.  In  other  words, 
nothing  has  been  produced  in  this  machine  for 
the  purpose  of  being  developed  later  into  some- 
thing of  value,  but  all  parts  that  have  been  pro- 
duced are  of  value  at  the  time  of  their  appearance. 
We  must,  in  short,  look  for  forces  constantly  in 


148  THE  STORY  OF  THE  LIVING  MACHINE. 

action  and  always  tending  in  the  same  direction 
of  greater  complexity  of  structure. 

Is  it  possible  to  discover  these  forces  and  com- 
prehend their  action  ? Before  the  modern  de- 
velopment of  evolution  this  question  would  un- 
hesitatingly have  been  answered  in  the  negative. 
To-day,  under  the  influence  of  the  descent  theory, 
stimulated,  in  the  first  place,  by  Darwin,  the 
question  will  be  answered  by  many  with  equal 
promptness  in  the  affirmative.  At  all  events,  we 
have  learned  in  the  last  forty  years  to  recognize 
some  of  the  factors  which  have  been  at  work  in 
the  construction  of  this  machine.  We  must  turn, 
therefore,  to  the  consideration  of  these  factors. 

Forces  at  Work  in  the  Building  of  the  Living 
Machine. — There  are  three  primary  factors  which 
lie  at  the  bottom  of  the  whole  process.  They 
are — 

1.  Reproduction , which  preserves  type  from  gen- 
eration to  generation. 

2.  Variation , which  modifies  type  from  genera- 
tion to  generation. 

3.  Heredity , which  transmits  characters  from 
generation  to  generation. 

Each  must  be  considered  by  itself. 

Reproduction. — Reproduction  is  the  primary 
factor  in  this  process  of  machine  building,  hered- 
ity and  variation  being  simply  phases  of  repro- 
duction. The  living  machine  has  developed  by 
natural  processes,  all  other  machines  by  artificial 
methods.  Reproduction  is  the  one  essential  point 
of  difference  between  the  living  machine  and  the 
others  which  has  made  their  construction  by 
natural  processes  a possibility.  What,  then,  is 
reproduction  ? Reproduction  is  in  all  cases  at 
the  bottom  simple  division.  Whether  we  consider 


THE  LIVING  MACHINE  BUILDING  FACTORS.  *149 

the  plant  that  multiplies  by  buds  or  the  unicellu- 
lar animal  that  simply  divides  into  two  equal 
parts,  or  the  larger  animal  that  multiplies  by 
eggs,  we  find  that  in  all  cases  the  fundamental 
feature  of  the  process  is  division.  In  all  cases 
the  organism  divides  into  two  or  more  parts,  each 
of  which  becomes  in  time  like  the  original. 
Moreover,  when  we  trace  this  division  further  we 
find  that  in  all  cases  it  is  to  be  referred  back  to 
the  division  of  the  cell,  such  as  we  have  described 
in  a previous  chapter.  The  egg  is  a single  cell 
which  has  come  from  the  parent  by  the  division 
of  one  of  the  cells  in  the  body  of  the  parent.  A 
bud  is  simply  a mass  of  cells  which  have  all  arisen 
from  the  parent  cells  by  division.  The  founda- 
tion of  reproduction  is  thus  in  all  cases  cell 
division.  Now,  this  process  of  division  is  depen- 
dent upon  the  properties  of  the  cell.  Firstly,  it  is 
a result  of  the  assimilative  powers  of  the  cell,  for 
only  through  assimilation  can  the  cell  increase  in 
size,  and  only  as  it  increases  in  size  can  it  gain 
sustenance  for  cell  division.  Secondly,  it  is  de- 
pendent, as  we  have  seen,  upon  the  mechanism 
of  the  cell  body,  and  especially  the  nucleus  and 
centrosome.  These  structures  regulate  the  cell 
division,  and  hence  the  reproduction  of  all  ani- 
mals and  plants.  We  can  not,  therefore,  find  any 
explanation  of  reproduction  until  we  have  ex- 
plained the  mechanism  of  the  cell.  The  funda- 
mental feature  of  nature’s  machine  building  is 
thus  based  upon  the  machinery  of  the  nucleus 
and  centrosome  of  the  organic  cell. 

Aside  from  the  simple  fact  that  it  preserves 
the  race,  the  most  important  feature  connected 
with  this  reproduction  is  its  wonderful  fruitful- 
ness. Since  it  results  from  division,  it  always 


150  THE  STORY  OF  THE  LIVING  MACHINE. 

tends  to  increase  the  offspring  in  geometrical 
ratio.  In  the  simplest  case,  that  of  the  unicellu- 
lar animals,  the  cell  divides,  giving  rise  to  two 
animals,  each  of  which  divides  again,  producing 
four,  and  these  again,  giving  eight,  etc.  The 
rapidity  of  this  multiplication  is  sometimes  incon- 
ceivable. It  depends,  of  course,  upon  the  inter- 
val of  time  between  the  successive  divisions,  but 
among  the  lower  organisms  this  interval  is  some- 
times not  more  than  half  an  hour,  the  result  of 
which  is  that  a single  individual  could  give  rise 
in  the  course  of  twenty-four  hours  to  sixteen 
million  offspring.  This  is  doubtless  an  extreme 
case,  but  among  all  the  lower  animals  the  rate  is 
very  great.  Among  larger  animals  the  process  is 
more  complicated  ; but  here,  too,  there  is  the  same 
tendency  to  geometrical  progression,  although  the 
intervals  between  the  successive  reproductions 
may  be  quite  long  and  irregular.  But  it  is  al- 
ways so  great  that  if  allowed  to  progress  unhin- 
dered at  its  normal  rate  the  offspring  would,  in 
a few  years,  become  so  numerous  as  to  crowd 
other  life  out  of  existence.  Even  the  slow-breed- 
ing elephant  would,  if  allowed  to  breed  unhin- 
dered for  seven  hundred  and  fifty  years,  produce 
nineteen  million  offspring — a rate  of  increase 
plainly  incompatible  with  the  continued  existence 
of  other  animals. 

Here,  then,  we  have  the  foundation  of  nature’s 
method  of  building  animals  and  plants  of  the 
higher  classes.  In  the  machinery  of  the  cell  she 
has  a power  of  reproduction  which  produces  an 
increase  in  geometrical  ratio  far  beyond  the  pos- 
sibility for  the  surface  of  the  earth  to  maintain. 

Heredity. — The  offspring  which  arise  by  these 
processes  of  division  are  like  each  other,  and  like 


THE  LIVING  MACHINE  BUILDING  FACTORS.  15 1 

the  parent  from  which  they  sprung.  This  is  the 
essence  of  what  is  called  heredity.  Its  signifi- 
cance in  the  process  of  machine  building  is  evi- 
dent at  once.  It  is  the  conserving  force  which 
preserves  the  forms  already  produced  and  makes 
it  possible  for  each  generation  to  build  upon  the 
structures  of  the  earlier  ones.  Without  it  each 
generation  would  have  to  begin  anew  at  the  be- 
ginning, and  nothing  could  be  accomplished.  But 
since  this  principle  brings  each  individual  to  the 
same  place  where  its  parents  stand,  and  thus 
always  builds  the  offspring  into  a machine  like 
the  parent,  it  makes  it  possible  for  the  successive 
generations  to  advance.  Heredity  is  thus  like  the 
power  of  memory,  or  better  still,  like  the  invention 
of  printing  in  the  development  of  civilization.  It 
is  a record  of  past  achievements.  By  means  of 
printing  each  age  is  enabled  to  benefit  by  the  dis- 
coveries of  the  previous  age,  and  without  it  the 
development  of  civilization  would  be  impossible. 
In  the  same  way  heredity  enables  each  generation 
to  benefit  by  the  achievements  of  its  ancestors  in 
the  process  of  machine  building,  and  thus  to  de- 
vote its  own  energies  to  advancement. 

The  fact  of  heredity  is  patent  enough.  It  has 
been  always  clearly  recognized  that  the  child  has 
the  characters  of  its  parents,  and  this  belief  is  so 
well  attested  as  to  need  no  proof.  It  is  still  a 
question  as  to  just  what  characters  may  be  in- 
herited, and  what  influences  may  affect  the  inher- 
itance. There  are  plenty  of  puzzling  problems 
connected  with  heredity,  but  the'  fact  of  heredity 
is  one  of  the  foundation  stones  of  biological 
science.  Upon  it  must  be  built  all  theories  which 
look  toward  the  explanation  of  the  origin  of  the 
living  machine. 

11 


152  THE  STORY  OF  THE  LIVING  MACHINE. 

This  factor  of  heredity  again  we  must  trace 
back  to  the  machinery  of  the  cell.  We  have  seen 
in  the  previous  pages  evidence  for  the  wonderful 
nature  of  the  chromosomes  of  the  cells.  We 
can  not  pretend  to  understand  them,  but  they 
must  be  extraordinarily  complex.  We  have  seen 
proof  that  these  chromosomes  are  probably  the 
physical  basis  of  heredity,  since  they  are  the  only 
parts  of  each  parent  which  are  handed  down  to 
subsequent  generations.  With  these  various  facts 
of  cell  division  and  cell  fertilization  in  mind,  we 
can  reach  a very  simple  explanation  of  funda- 
mental features  of  heredity.  The  following  is  an 
outline  of  the  most  widely  accepted  view  of  the 
hereditary  process. 

Recognizing  that  the  chromosomes  are  the 
physical  basis  of  hereditary  transmission,  we  can 
picture  to  ourselves  the  transmission  of  hereditary 
characters  somethingas  follows  : As  we  have  seen, 
the  fertilized  egg  contains  an  equal  number  of 
chromosomes  from  each  parent  (Fig.  42).  Now 
when  this  fertilized  cell  divides,  each  of  the  rods 
splits  lengthwise,  half  of  each  entering  each  of 
the  two  cells  arising  from  the  cell  division.  From 
this  method  of  division  of  the  chromosomes  it 
follows  that  the  daughter  cells  would  be  equiva- 
lent to  each  other  and  equivalent  also  to  the  un- 
divided egg.  If  the  original  chromosomes  con- 
tained potentially  all  the  hereditary  traits  handed 
down  from  parent  to  child,  the  chromosomes  of 
each  daughter  cell  will  contain  similar  hereditary 
traits.  If,  therefore,  the  original  fertilized  egg 
possessed  the  power  of  developing  into  an  adult 
like  the  parent,  each  of  the  daughter  cells  should 
likewise  possess  the  power  of  developing  into  a 
similar  adult.  And  thus  each  cell  which  arises  as 


THE  LIVING  MACHINE  BUILDING  FACTORS.  153 

the  result  of  such  division  should  possess  similar 
characters  so  long  as  this  method  of  division  con- 
tinues. But  after  a little  in  the  development  of 
the  egg  a differentiation  among  the  daughter  cells 
arises.  They  begin  to  acquire  different  shapes  and 
different  functions.  This  we  can  only  believe  to 
be  the  result  of  a differentiation  in  their  chro- 
matin material.  In  the  cell  division  the  chromo- 
somes no  longer  split  into  equivalent  halves,  but 
some  characters  are  portioned  off  to  some  cells 
and  others  to  other  cells.  Those  cells  which  are 
to  carry  on  digestive  functions  when  they  are 
formed  receive  chromatin  material  which  especially 
controls  them  in  the  performance  of  this  diges- 
tive function,  while  those  which  are  to  produce 
sensory  organs  receive  a different  portion  of  the 
chromatin  material.  Thus  the  adult  individual 
is  built  up  as  the  cells  receive  different  portions 
of  this  hereditary  substance  contained  in  the 
original  chromosomes.  The  original  chromosomes 
contained  all  hereditary  characters,  but  as  devel- 
opment proceeds  these  are  gradually  portioned 
out  among  the  daughter  cells  until  the  adult  is 
formed. 

From  this  method  of  division  it  will  be  seen 
that  each  cell  of  the  adult  does  not  contain  all 
the  characters  concealed  in  the  original  chro- 
mosomes of  the  egg,  although  each  contains  a 
part  which  may  have  been  derived  from  each 
parent.  It  is  thought,  however,  that  a part  of 
the  original  chromatin  material  does  not  thus 
become  differentiated,  but  remains  entirely  un- 
changed as  the  individual  is  developing.  This 
chromatin  material  may  increase  in  amount  by 
assimilation,  but  it  remains  unchanged  during  the 
entire  growth  of  the  individual.  It  thus  follows 


154  THE  story  of  the  living  machine. 

that  the  adult  will  contain,  along  with  its  differ- 
entiated material,  a certain  amount  of  the  origi- 
nal physical  basis  of  heredity  which  still  retains 
its  original  powers.  This  undifferentiated  chro- 
matin material  originally  possessed  powers  of  pro- 
ducing a new  individual,  and  of  course  it  still 
possesses  these  powers,  since  it  has  remained  dor- 
mant without  alteration.  Further,  it  will  follow 
that  if  this  dormant  undifferentiated  chromatin 
should  start  into  activity  and  produce  a new  in- 
dividual, the  new  individual  thus  produced  would 
be  identical  in  all  characters  with  the  one  which 
actually  did  develop  from  the  egg,  since  both  in- 
dividuals would  have  come  from  a bit  of  the  same 
chromatin.  The  child  woulj  be  like  the  parent. 
This  would  be  true  no  matter  how  much  this  un- 
differentiated material  should  increase  in  amount 
by  assimilation,  so  long  as  it  remained  unaltered  in 
character,  and  it  hence  follows  that  every  indi- 
vidual carries  around  a certain  amount  of  undif- 
ferentiated chromatin  material  in  all  respects  iden- 
tical with  that  from  which  he  developed. 

Now  whether  this  undifferentiated  germ  plasm, 
as  we  will  now  call  it,  is  distributed  all  over  the 
body,  or  is  collected  at  certain  points,  is  imma- 
terial to  our  purpose.  It  is  certain  that  portions 
of  it  find  their  way  into  the  reproductive  organs 
of  the  animal  or  plant.  Thus  we  see  that  part  of 
the  chromatin  material  in  the  egg  of  the  first  gen- 
eration develops  into  the  second  generation,  while 
another  part  of  it  remains  dormant  in  that  second 
generation,  eventually  becoming  the  chromatin  of 
its  eggs  and  spermatozoa.  Thus  each  egg  of  the 
second  generation  receives  chromosomes  which 
have  come  directly  from  the  first  generation,  and 
thus  it  will  follow  that  each  of  these  eggs  will 


THE  LIVING  MACHINE  BUILDING  FACTORS.  155 

have  identical  properties  with  the  egg  of  the  first 
generation.  Hence  if  one  of  these  new  eggs  de- 
velops into  an  adult  it  will  produce  an  adult  ex- 
actly like  the  second  generation,  since  it  contains 
chromosomes  which  are  absolutely  identical  with 
those  from  which  the  second  generation  sprung. 
There  is  thus  no  difficulty  in  understanding  why 
the  second  generation  will  be  like  the  first,  and 
since  the  process  is  simply  repeated  again  in  the 
next  reproduction,  the  third  generation  will  be 
like  the  second,  and  so  on,  generation  after  gen- 
eration. A study  of  the  accompanying  diagram 
will  make  this  clear. 

In  other  words,  we  have  here  a simple  undeu 
standing  of  at  least  some  of  the  features  of  hered- 
ity. This  explanation  is  that  some  of  the  chro- 
matin material  or  germ  plasm  is  handed  down 
from  one  generation  to  another,  and  is  stored 
temporarily  in  the  nucleii  of  the  reproductive 
cells.  During  the  life  of  the  individual  this  germ 
plasm  is  capable  of  increasing  in  amount  without 
changing  its  nature,  and  it  thus  continues  to  grow 
and  is  handed  down  from  generation  to  genera- 
tion, always  endowed  with  the  power  of  develop- 
ing into  a new  individual  under  proper  conditions, 
and  of  course  when  it  does  thus  give  rise  to  new 
individuals  they  will  all  be  alike.  We  can  thus 
easily  understand  why  a child  is  like  its  parent. 
It  is  not  because  the  child  can  inherit  directly 
from  its  parent,  but  rather  because  both  child 
and  parent  have  come  from  the  unfolding  of  two 
bits  of  the  same  germ  plasm.  This  fact  of  the 
transmission  of  the  hereditary  substance  from 
generation  to  generation  is  known  as  the  theory 
of  the  continuity  of  germ  plasm. 

Such  appears  to  be,  at  least  in  part,  the  ma- 


156  THE  STORY  OF  THE  LIVING  MACHINE. 


chinery  of  heredity.  This  understanding  makes 
the  germ  substance  perpetual  and  continuous,. 


A represents  an  egg 
of  a starfish.  From 
one  half;  the  unshaded 
portion,  develops  the 
starfish  cf  the  next 
generation,  B.  The 
other  is  distributed 
without  change  in  the 
ovaries,  ov , of  the  in- 
dividual, B.  From 
these  ovaries  arises  the 
next  egg,  A\  with  its 
germ  plasm.  This 
germ  plasm  is  evident- 
ly identical  v ith  that  in 
A , since  it  is  merely  a 
bit  of  the  same  handed 
down  through  the  indi- 
vidual, B.  In  the  de- 
velopment of  the  next 
generation  the  process 
is  repeated,  and  hence 
B'  will  be  like  B , and 
the  third  generation  of 
eggs  identical  with 
the  first  and  second. 
The  undifferentiated 
part  of  the  germ  plasm 
is  thus  simply  handed 
on  from  one  genera- 
tion to  the  next. 


Fig.  50. — Diagram  illustrating  the  principle  of  heredity. 


and  explains  why  successive  generations  are  alike 
It  does  not  explain,  indeed,  why  an  individual  in- 


THE  LIVING  MACHINE  BUILDING  FACTORS.  157 

herits  from  its  parents,  but  why  it  is  like  its 
parents.  While  biologists  are  still  in  dispute 
over  many  problems  connected  with  heredity, 
all  are  agreed  to-day  that  this  principle  of  the 
continuity  of  the  heredity  substance  must  be  the 
basis  of  all  attempts  to  understand  the  machinery 
of  heredity.  But  plainly  this  whole  process  is  a 
function  of  the  cell  machinery.  While,  therefore, 
the  idea  of  the  continuity  of  germ  substance 
greatly  simplifies  our  problem,  we  must  acknowl- 
edge that  once  more  we  are  thrown  back  upon 
the  mysteries  of  the  cell.  Until  we  can  more 
fully  explain  the  cell  machine  we  must  recognize 
our  inability  to  solve  the  fundamental  question 
of  why  an  individual  is  like  its  parents. 

But  plainly  reproduction  and  heredity,  as  we 
have  thus  far  considered  them,  will  be  unable  to 
account  for  the  slow  modification  of  the  machine; 
for  in  accordance  with  the  facts  thus  far  outlined, 
each  generation  would  be  precisely  like  the  last , and 
there  would  be  no  chance  for  development  and 
change  from  generation  to  generation.  If  the 
individual  is  simply  the  unfolding  of  the  powers 
possessed  by  a bit  of  germ  plasm,  and  if  this 
germ  plasm  is  simply  handed  on  from  generation 
to  generation,  the  successive  generations  must  of 
necessity  be  identical.  But  the  living  machine 
has  been  built  by  changes  in  the  successive  gen- 
eration, and  hence  plainly  some  other  factor  is 
needed.  This  factor  is  variation. 

Variation. — Variation  is  the  principle  that  pro- 
duces modification  of  type.  Heredity,  as  just  ex- 
plained, would  make  all  generations  alike.  But 
nothing  is  more  certain  than  that  they  are  not 
alike.  The  fact  of  variation  #is  patent  on  every 
side,  for  no  two  individuals  are  alike.  Successive 


158  THE  STORY  OF  THE  LIVING  MACHINE. 

generations  differ  from  each  other  in  one  respect 
or  another.  Birds  vary  in  the  length  of  their 
bills  or  toes;  butterflies,  in  their  colours;  dogs, 
in  their  size  and  shape  and  markings;  and  so 
on  through  an  endless  category.  Plants  and 
animals  alike  throughout  nature  show  variations 
in  the  greatest  profusion.  It  is  these  variations 
which  must  furnish  us  with  the  foundation  of  the 
changes  which  have  gradually  built  up  the  living 
machine. 

Of  the  fact  of  these  variations  there  is  no 
question,  and  the  matter  need  not  detain  us. 
Every  one  has  had  too  many  experiences  to  ask 
for  proof.  Of  the  nature  of  the  variations,  how- 
ever, there  are  some  points  to  be  considered  which 
are  very  germane  to  our  subject.  In  the  first  place, 
we  must  notice  that  these  variations  are  of  two 
kinds.  There  is  one  class  which  is  born  with  the 
individual,  so  that  they  are  present  from  the  time 
of  birth.  In  saying  that  these  variations  are  born 
with  the  individual  we  do  not  necessarily  mean 
that  they  are  externally  apparent  at  birth.  A 
child  may  inherit  from  its  parents  characters  which 
do  not  appear  till  adult  life.  For  example,  a child 
may  inherit  the  colour  of  its  father’s  hair,  but  this 
colour  is  not  apparent  at  birth.  It  appears  only 
in  later  life,  but  it  is  none  the  less  an  inborn 
character.  In  the  same  way,  we  may  have  many 
inborn  variations  among  individuals  which  do 
not  make  themselves  seen  until  adult  life,  but 
which  are  none  the  less  innate.  The  offspring  of 
the  same  parents  may  show  decided  differences, 
although  they  are  put  under  similar  conditions, 
and  such  differences  are  of  course  inherent  in 
the  nature  of  the  individual.  Such  variations  are 
called  congenital  variations. 


THE  LIVING  MACHINE  BUILDING  FACTORS.  159 

There  is,  however,  a second  class  of  variations 
which  are  not  born  in  the  individual,  but  which 
arise  as  the  result  of  some  conditions  affecting  its 
after-life.  The  most  extreme  instances  of  this 
kind  are  mutilations.  Some  men  have  only  one 
leg  because  the  other  has  been  lost  by  accident. 
Here  is  a variation  acquired  as  the  result  of 
circumstances.  A blacksmith  differs  from  other 
members  of  his  race  in  having  exceptionally  large 
arm  muscles;  but  here,  again,  the  large  muscles 
have  been  produced  by  use.  A European  who 
has  lived  under  a tropical  sun  has  a darkened 
skin,  but  this  skin  has  evidently  been  darkened 
by  the  action  of  the  sun,  and  is  quite  a different 
thing  from  the  dark  skin  of  the  dark  races  of 
men.  In  such  instances  we  have  variations  pro- 
duced in  individuals  as  the  result  of  outside  influ- 
ences acting  upon  them.  They  are  not  inborn, 
but  are  secondarily  acquired  by  each  individual. 
We  call  them  acquired  variations. 

It  is  not  always  possible  to  distinguish  be- 
tween these  two  types  of  variation.  Frequently 
a character  will  be  found  in  regard  to  which  it  is 
impossible  to  determine  whether  it  is  congenital- 
or  acquired.  If  a child  is  born  under  the  tropical 
sun,  how  can  we  tell  whether  its  dark  skin  was 
the  result  of  direct  action  of  the  sun  on  its  own 
skin,  or  was  an  inheritance  from  its  dark-skinned 
parents?  We  might  suppose  that  this  could  be 
answered  by  taking  a similar  child,  bringing  it  up 
away  from  the  tropical  sun,  and  seeing  whether 
his  skin  remained  dark.  This  would  not  suffice, 
however;  for  if  such  a child  did  then  develop  a 
white  skin,  we  could  not  tell  but  that  this  lighter- 
coloured  skin  had  been  produced  by  the  direct 
bleaching  effect  of  the  northern  climate  upon  a 


160  THE  STORY  OF  THE  LIVING  MACHINE. 

skin  which  otherwise  would  have  been  dark.  In 
other  words,  a conclusive  answer  can  not  here  be 
given.  It  is  not  our  purpose,  however,  to  attempt 
to  distinguish  between  these  two  kinds  of  varia- 
tions, but  simply  to  recognize  that  they  occur. 

Our  next  problem  must  be  to  search  for  an  ex- 
planation of  these  variations.  With  the  acquired 
variations  we  have  no  particular  trouble,  for  they 
are  easily  explained  as  due  to  the  direct  action  of 
the  environment  upon  animals.  One  of  the  fun- 
damental characters  of  the  living  protoplasm 
(using  the  word  now  in  its  widest  sense)  is  its 
extreme  instability,  So  unstable  is  it  that  any 
disturbing  influence  will  affect  it.  If  two  similar 
unicellular  organisms  are  placed  under  different 
conditions  they  become  unlike,  since  their  un- 
stable protoplasm  is  directly  affected  by  the  sur- 
rounding conditions.  With  higher  animals  the 
process  is  naturally  a little  more  complicated ; 
but  here,  too,  they  are  easily  understood  as  part 
of  the  function  of  the  machine.  One  of  the  ad- 
justments of  the  machine  is  such  that  when  any 
organ  is  used  more  than  usual  the  whole  machine 
reacts  in  such  a way  as  to  send  more  blood  to 
this  special  organ.  The  result  is  a change  in  the 
nutrition  of  the  organ  and  a corresponding  varia- 
tion in  the  individual.  Thus  acquired  variations 
are  simply  functions  of  the  action  of  the  machine. 

Congenital  variations,  however,  can  not  re- 
ceive such  an  explanation.  Being  born  with  the 
individual,  they  can  not  be  produced  by  condi- 
tions affecting  him,  but  rather  to  something  affect- 
ing the  germ  plasm  from  which  he  sprung.  The 
nature  of  the  germ  plasm  controls  the  nature  of 
the  individual,  and  congenital  variations  must 
consequently  be  due  to  its  variations.  But  it  is 


THE  LIVING  MACHINE  BUILDING  FACTORS.  161 

not  so  easy  to  see  how  this  germ  plasm  can  un- 
dergo variation.  The  conditions  which  surround 
the  individual  would  affect  its  body,  but  it  is  not 
easy  to  believe  that  they  would  affect  the  ger- 
minal substance.  Indeed,  it  is  not  easy  to  see  how 
any  external  conditions  can  have  influence  upon 
this  germinal  material  if  it  is  not  an  active  part 
of  the  body,  but  is  simply  stored  within  it  for  fu- 
ture use  in  reproduction.  How  could  any  changes 
in  the  environment  of  the  individual  have  any  ef- 
fect upon  this  dormant  material  stored  within  it  ? 
But  if  we  are  correct  in  regarding  this  germ  mate- 
rial in  the  reproductive  bodies  as  the  basis  of 
heredity  and  the  guiding  force  in  development, 
then  it  follows  that  the  only  way  in  which  con- 
genital variations  can  occur  is  by  some  variations 
in  the  germ  plasm.  If  a child  developed  from 
germ  plasm  identical  with  that  from  which  its 
parents  developed,  it  would  inherit  identical  char- 
acters; and  if  there  are  any  congenital  variations 
from  its  parents,  they  must  be  due  to  some  varia- 
tions in  the  germ  plasm.  In  other  words,  in  order 
to  explain  congenital  variations  we  must  account 
for  variations  in  the  germ  plasm. 

Now,  there  are  two  methods  by  which  we  may 
suppose  that  these  variations  in  the  germ  may 
arise.  The  first  is  by  the  direct  influence  upon 
the  germ  plasm  of  certain  unknown  external 
conditions.  The  life  substance  of  organisms  is 
always  very  unstable,  and,  as  we  have  seen,  ac- 
quired variations  are  caused  by  external  influ- 
ences directly  affecting  it.  Now,  the  hereditary 
material  is  also  life  substance,  and  it  is  plainly  a 
possibility  for  us  to  imagine  that  this  germ  mate- 
rial is  also  subject  to  influences  from  the  condi- 
tions surrounding  it.  That  such  variations  do 


1 62  THE  STORY  OF  THE  LIVING  MACHINE. 

occur  appears  to  be  hardly  doubtful,  although  we 
do  not  know  what  sort  of  influences  can  produce 
them.  If  the  germ  plasm  is  wholly  stored  within 
the  reproductive  gland,  it  is  certainly  in  a position 
to  be  only  slightly  affected  by  surrounding  con- 
ditions which  affect  the  animal.  We  can  readily 
understand  that  the  use  of  an  organ  like  the  arm 
will  affect  it  in  such  a way  as  to  produce  changes 
in  its  protoplasm,  but  we  can  hardly  imagine  that 
such  use  of  the  arm  would  produce  any  change 
in  the  hereditary  substance  which  is  stored  in  the 
reproductive  organs.  External  conditions  may 
thus  readily  affect  the  body,  but  not  so  readily 
the  germ  material.  Even  if  such  material  is  dis- 
tributed more  or  less  over  the  body  instead  of 
being  confined  to  the  reproductive  glands,  as 
some  believe,  the  difficulty  is  hardly  lessened. 
This  difficulty  of  understanding  how  the  germ 
plasm  can  be  affected  by  external  conditions  has 
led  one  school  of  biologists  to  deny  that  it  is  sub- 
ject to  any  variation  by  external  conditions,  and 
hence  that  all  modification  of  the  germ  plasm 
must  come  from  some  other- source.  Probably  no 
one,  however,  holds  this  position  to-day,  and  it  is 
the  general  belief  that  the  germ  plasm  may  be  to 
some  slight  extent  modified  by  external  conditions. 
Of  course,  if  such  variations  do  occur  in  the  germ 
plasm  they  will  become  congenital  variations  of 
the  next  generation,  since  the  next  generation  is 
the  unfolding  of  the  germ  plasm. 

The  second  method  by  which  the  variations  of 
germ  plasm  may  arise  is  apparently  of  more  im- 
portance. It  is  based  upon  the  fact  that,  with 
all  higher  animals  and  plants  at  least,  each  indi- 
vidual has  two  parents  instead  of  one.  In  our 
study  of  cells  we  have  seen  that  the  machinery 


TIIE  LIVING  MACHINE  BUILDING  FACTORS.  1 63 

of  the  cell  is  such  that  it  requires  in  the  ordinary 
process  of  reproduction  the  union  of  germinal 
material  from  two  different  individuals  to  pro- 
duce a cell  which  can  develop  into  a new  indi- 
vidual. As  we  have  seen,  the  egg  gets  rid  of  half 
its  chromosomes  in  order  to  receive  an  equal 
number  from  a male  parent;  and  thus  the  fer- 
tilized egg  contains  chromosomes,  and  hence 
hereditary  material,  from  two  different  individ- 
uals. Now,  this  sexual  reproduction  occurs  very 
widely  in  the  organic  world.  Among  some  of 
the  lowest  forms  of  unicellular  organisms  it  is 
not  known,  but  in  most  others  some  form  of  such 
union  is  universal.  Now,  here  is  plainly  an  abun- 
dant opportunity  for  congenital  variations;  for 
it  is  seen  that  each  individual  does  not  come  from 
germ  material  identical  unth  that  from  which  either 
parent  came , but  from  some  of  this  material  mixed 
with  a similar  amount  from  a different  parent.  Now, 
the  two  parents  are  never  exactly  alike,  and  hence 
the  germ  plasm  which  each  contributes  to  the  off- 
spring will  not  be  exactly  alike.  The  offspring 
will  thus  be  the  result  of  the  unfolding  of  a bit 
of  germ  plasm  which  will  be  different  from  that 
from  which  either  of  its  parents  developed,  and 
these  differences  will  result  in  congenital  variations. 
Sexual  reproduction  thus  results  in  congenital 
variations;  and  if  congenital  variations  are  neces- 
sary for  the  evolution  of  the  living  machine — and 
we  shall  soon  see  reason  for  believing  that  they 
are — we  find  that  sexual  reproduction  is  a device 
adopted  for  bringing  out  such  congenital  varia- 
tions. 

Inheritance  of  Variations. — The  reason  why 
congenital  variations  are  needed  for  the  evolution 
of  the  living  machine  is  clear  enough.  Evanescent 


164  THE  STORY  OF  THE  LIVING  MACHINE. 

variations  can  have  no  effect  upon  this  machine, 
for  they  would  disappear  with  the  individual  in 
which  they  appeared.  In  order  that  they  should 
have  any  influence  in  the  process  of  machine 
building  they  must  be  permanent  ones;  or,  in 
other  words,  they  must  be  inherited  from  genera- 
tion to  generation.  Only  as  such  variations  are 
transmitted  by  heredity  can  they  be  added  to  the 
structure  of  the  developing  machine.  Therefore 
we  must  ask  whether  the  variations  are  inherited. 

Jn  regard  to  the  congenital  variations  there 
can  be  no  difficulty.  The  very  fact  that  they  are 
congenital  shows  us  that  they  have  been  produced 
by  variations  in  the  germ  plasm,  and  as  such  they 
must  be  transmitted,  not  only  to  the  next  genera- 
tion, but  to  all  following  generations,  until  the 
germ  plasm  becomes  again  modified.  This  germ 
plasm  is  handed  on  from  generation  to  genera- 
tion with  all  its  variations,  and  hence  the  varia- 
tions will  be  added  permanently  to  the  machine. 
Congenital  variations  are  thus  a means  for  per- 
manently modifying  the  organism,  and  by  their 
agency  must  we  in  large  measure  believe  that 
evolution  through  the  ages  has  taken  place. 

With  the  acquired  variations  the  matter  stands 
quite  differently.  We  can  readily  understand 
how  influences  surrounding  an  animal  may  affect 
its  organs.  The  increase  in  the  size  of  the 
muscles  of  the  blacksmith’s  arm  by  use  we  under- 
stand readily  enough.  But  with  our  understand- 
ing of  the  machinery  of  heredity  we  can  not  see 
how  such  an  effect  can  extend  to  the  next  gener- 
ation. It  is  only  the  organ  directly  affected 
that  is  modified  by  external  conditions.  Ac- 
quired variations  will  appear  in  the  part  of  the 
body  influenced  by  the  changed  conditions.  But 


THE  LIVING  MACHINE  BUILDING  FACTORS.  165 

the  germ  plasm  within  the  reproductive  glands 
is  not,  so  far  as  we  can  see,  subject  to  the  influ- 
ence of  an  increased  use,  for  example,  in  the  arm 
muscles.  The  germ  material  is  derived  from  the 
parents,  and,  if  it  is  simply  stored  in  the  individ- 
ual, how  could  an  acquired  variation  affect  it  ? If 
an  individual  lose  a iimb  his  offspring  will  not  be 
without  a corresponding  limb,  for  the  hereditary 
material  is  in  the  reproductive  organs,  and  it  is 
impossible  to  believe  that  the  loss  of  the  limb  can 
remove  from  the  hereditary  material  in  the  repro- 
ductive glands  just  that  part  of  the  germ  plasm 
which  was  designed  for  the  production  of  the 
limb.  So,  too,  if  the  germ  plasm  is  simply  stored 
in  the  individual,  it  is  impossible  to  conceive  any 
way  that  it  can  be  affected  by  the  conditions 
around  the  individual  in  such  a way  as  to  explain 
the  inheritance  of  acquired  variations.  If  ac- 
quired variations  do  not  affect  the  germ  plasm 
they  cannot  be  inherited,  and  if  the  germ  plasm 
is  only  a bit  of  protoplasmic  substance  handed 
down  from  generation  to  generation,  we  can  not 
believe  that  acquired  variations  can  influence  it. 

From  such  considerations  as  these  have  arisen 
two  quite  different  views  among  biologists  ; and, 
while  it  is  not  our  purpose  to  deal  with  disputed 
points,  these  views  are  so  essential  to  our  subject 
that  they  must  be  briefly  referred  to.  One  class 
of  biologists  adhere  closely  to  the  view  already 
outlined,  and  insist  for  this  reason  that  acquired 
variations  can  not  under  any  conditions  be  in- 
herited. They  insist  that  all  inherited  variations 
are  congenital,  and  due  therefore  to  direct  varia- 
tions in  the  germ  plasm,  and  that  all  instances  of 
seeming  inheritance  of  acquired  variations  are 
capable  of  other  explanation.  The  other  school 


1 66  THE  STORY  OF  THE  LIVING  MACHINE. 

is  equally  insistent  that  there  are  abundant  in- 
stances of  the  inheritance  of  acquired  characters, 
claiming  that  these  proofs  are  so  strong  as  to 
demand  their  acceptance.  Hence  this  class  of 
biologists  insist  that  the  explanation  of  heredity 
given  as  a simple  handing  down  from  generation 
to  generation  of  a germ  plasm  is  not  complete, 
and  that  while  it  is  doubtless  the  foundation  of 
heredity,  it  must  be  modified  in  some  way  so  as 
to  admit  of  the  inheritance  of  acquired  characters. 

There  is  no  question  that  has  excited  such  a 
wide  interest  in  the  biological  world  during  the 
last  fifteen  years  as  this  one  of  the  inheritance  of 
acquired  characters.  Until  about  1884  the  ques- 
tion was  not  seriously  raised.  Heredity  was 
known  to  be  a fact,  and  it  was  believed  that  while 
congenital  characters  are  more  commonly  in- 
herited, acquired  characters  may  also  frequently 
be  handed  down  from  generation  to  generation. 
The  facts  which  we  have  noted  of  the  contin- 
uity of  germ  plasm  have  during  the  last  fifteen 
years  led  many  biologists  to  deny  the  possibility 
of  the  latter.  The  debate  which  arose  has  con- 
tinued vigorously,  and  can  not  be  regarded  as 
settled  at  the  present  time.  One  result  of  this 
debate  is  clear.  It  has  been  shown  beyond 
question  that  while  the  inheritance  of  congenital 
characters  is  the  rule,  the  inheritance  of  acquired 
characters  is  at  all  events  unusual.  At  the 
present  time  many  naturalists  would  be  inclined 
to  think  that  the  balance  of  evidence  indicates 
that  under  certain  conditions  certain  kinds  of 
acquired  characters  may  be  inherited,  although 
this  is  still  disputed  by  others.  Into  this  discus- 
sion we  cannot  enter  here.  The  reason  for  refer- 
ring to  it  at  all  is,  however,  evident.  We  are 


THE  LIVING  MACHINE  BUILDING  FACTORS.  167 

searching  for  nature's  method  of  building  ma- 
chines. It  is  perfectly  clear  that  variations 
among  animals  and  plants  are  the  foundations  of 
the  successive  steps  in  advance  made  in  this 
machine  building,  but  of  course  only  such  varia- 
tions as  can  be  transmitted  to  posterity  can 
serve  any  purpose  in  this  development.  If  there- 
fore it  should  prove  that  acquired  characters  can 
not  be  inherited,  then  we  should  no  longer  be  able 
to  look  upon  the  direct  influence  of  the  surround- 
ings as  a factor  in  the  machine  building.  We 
should  then  have  nothing  left  except  the  congeni- 
tal variations  produced  by  sexual  union,  or  the 
direct  variation  of  the  germ  plasm  as  a factor  for 
advance.  If,  however,  it  shall  prove  that  acquired 
characters  may  even  occasionally  be  inherited, 
then  the  direct  effect  of  the  environment  upon  the 
individual  will  serve  as  a decided  assistance  in 
our  problem. 

Here,  then,  we  have  before  us  the  factors 
which  have  been  concerned  in  the  building  of  the 
living  machine  under  nature’s  hands.  Reproduc- 
tion keeps  in  existence  a constantly  active,  un- 
stable, readily  modified  organism  as  a basis  upon 
which  to  build.  Variation  offers  constantly  new 
modifications  of  the  type,  while  heredity  insures 
that  the  modifications  produced  in  the  machine 
by  the  influences  which  give  rise  to  the  variations 
shall  be  permanently  fixed. 

Method  of  Machine  Building. — Natural  Selec- 
tion. The  method  by  which  these  factors  have 
worked  together  to  build  up  the  living  machines 
is  easily  understood  in  its  general  aspects,  al- 
though there  are  many  details  as  yet  unsolved. 
The  general  facts  connected  with  the  evolution 
of  animals  are  matters  of  common  knowledge. 

12 


1 68  THE  STORY  OF  THE  LIVING  MACHINE. 

We  need  do  no  more  than  outline  the  subject, 
since  it  is  well  understood  by  all.  The  basis  of 
the  method  is  natural  selection , which  acts  in  this 
machine  building  something  as  follows  : 

The  law  of  reproduction,  as  we  have  seen,  pro- 
duces new  individuals  with  extraordinary  rapidity, 
and  as  a result  more  individuals  are  born  than 
can  possibly  find  sustenance  in  the  world.  Hence 
only  a few  of  the  offspring  of  any  animal  or  plant 
can  live  long  enough  to  produce  offspring  in  turn. 
The  many  must  die  that  the  few  may  live;  and 
there  is,  therefore,  a constant  struggle  among  the 
individuals  that  are  born  for  food  or  for  room  in 
the  world.  In  this  struggle  for  existence  of  course 
the  weakest  will  go  to  the  wall,  while  those  that 
are  best  adapted  for  their  place  in  life  will  be  the 
ones  to  get  food,  live,  and  reproduce  their  kind. 
This  is  at  all  events  true  among  the  lower  animals, 
although  with  mankind  the  law  hardly  applies. 
Now,  among  the  individuals  that  are  born  there 
will  be  no  two  exactly  alike,  since  variations  are 
universal,  many  of  which  are  congenital  and  thus 
born  with  the  individual  and  transmitted  by  in- 
heritance. Clearly  enough  those  animals  that 
have  a variation  which  makes  them  a little  better 
adapted  for  the  struggle  will  be  the  ones  to  live 
and  hence  to  produce  offspring,  while  those  with- 
out such  advantage  will  be  the  ones  to  die.  We 
may  suppose,  for  example,  that  some  of  the  indi- 
viduals had  longer  necks  than  the  average.  In 
time  of  scarcity  of  food  these  individuals  would 
be  able  to  get  food  that  the  short-necked  indi- 
viduals could  not  reach.  Hence  in  times  of 
famine  the  long-necked  individuals  would  be  the 
ones  to  survive.  Now  if  this  peculiarity  were  a 
congenital  variation  it  would  be  already  repre- 


THE  LIVING  MACHINE  BUILDING  FACTORS.  169 

sented  in  the  germ  plasm,  and  consequently  it 
would  be  inherited  by  the  next  generation.  The 
short-necked  individuals  being  largely  destroyed 
in  this  struggle  for  food,  it  would  follow  that  the 
next  generation  would  be  a little  better  off  than 
the  last,  since  all  would  inherit  this  tendency  to- 
ward a long  neck.  A few  generations  would  then 
see  the  disappearance  of  all  individuals  which  did 
not  show  either  this  or  some  other  corresponding 
advantage,  and  in  this  way  the  lengthened  neck 
would  be  added  permanently  as  a part  of  the  ma- 
chine. When  this  time  came  this  peculiarity 
would  no  longer  give  its  possessors  any  advan- 
tage over  its  rivals,  since  all  would  possess  it. 
Now,  therefore,  some  new  variation  would  in  the 
same  way  determine  which  animals  should  live 
and  which  should  die  in  the  struggle,  and  in  time 
a new  modification  would  be  added  to  the  ma- 
chine. And  thus  this  process  continues,  one 
variation  after  another  being  added,  until  the 
machine  is  slowly  built  into  a more  and  more 
complicated  structure,  always  active  but  with  a 
constantly  increasing  efficiency.  The  construc- 
tion is  a natural  one.  A mixing  of  germ  plasm  in 
sexual  reproduction  or  some  other  agencies  pro- 
duce congenital  variations  ; natural  selection  act- 
ing upon  the  numerous  progeny  selects  the  best 
of  the  new  variations,  and  heredity  preserves  and 
hands  them  down  to  posterity. 

All  students  of  whatever  school  recognize  the 
force  of  this  principle  and  look  upon  natural  se- 
lection as  an  efficient  agency  in  machine  build- 
ing. It  is  probably  the  most  fundamental  of 
the  external  laws  that  have  guided  the  process. 
There  are,  however,  certain  other  laws  which 
have  played  a more  or  less  subordinate  part.  The 


170  THE  STORY  OF  THE  LIVING  MACHINE. 

chief  of  these  are  the  influence  of  migration  and 
isolation,  and  the  direct  influence  of  the  environ- 
ment. Each  of  these  laws  has  its  own  school  of 
advocates,  and  each  has  been  given  by  its  advo- 
cates the  chief  role  in  the  process  of  machine 
building. 

Migration  and  Isolation. — The  production  of  the 
various  types  of  machines  has  been  undoubtedly 
facilitated  by  the  migrations  of  animals  and  the 
isolation  of  different  groups  of  descendants  from 
each  other  by  various  natural  barriers.  The  vari- 
ations which  occur  in  organisms  are  so  great  that 
they  would  sometimes  run  into  abnormal  struc- 
tures were  it  not  for  the  fact  that  sexual  repro- 
duction constantly  tends  to  reduce  them.  In  an 
open  country  where  animals  and  plants  interbreed 
freely,  it  will  commonly  happen  that  individuals 
with  certain  peculiarities  will  mate  with  others 
without  such  peculiarities,  and  the  offspring  will 
therefore  inherit  the  peculiarity  not  in  increased 
degree  but  in  decreased  degree.  This  constant 
interbreeding  of  individuals  will  tend  to  prevent 
the  formation  of  many  modifications  in  the  ma- 
chine which  become  started  by  variations.  Now 
plainly  if  some  such  individuals,  with  a peculiar 
variation,  should  migrate  into  a new  territory  or 
become  isolated  from  their  relatives  which  do 
not  have  similar  variations,  these  individuals  will 
be  obliged  to  breed  with  each  other.  The  result 
will  be  that  the  next  generation,  arising  thus  from 
two  parents  each  of  which  shows  the  same  varia- 
tion, will  show  it  also  in  equal  or  increased  degree. 
Migrations  and  isolations  will  thus  tend  to  fix  in 
the  machine  variations  which  sexual  union  or 
other  influences  inaugurate.  Now  in  the  history 
of  the  earth’s  surface  there  have  been  many 


THE  LIVING  MACHINE  BUILDING  FACTORS.  1 7 1 

changes  which  tend  to  bring  about  such  migra- 
tion and  isolations,  and  this  factor  has  doubtless 
played  a more  or  less  important  part  in  the 
building  of  the  machines.  How  great  a part  we 
cannot  say,  nor  is  it  necessary  for  our  purpose 
to  decide;  for  in  all  these  cases  the  machine 
building  has  only  been  the  result  of  the  heredi- 
tary transmission  of  congenital  variation  under 
certain  peculiar  conditions.  The  fundamental 
process  is  the  same  as  already  considered,  only 
the  details  of  its  working  being  in  question. 

Direct  Influence  of  the  Environment. — Under 
this  head  we  have  a subject  of  great  importance. 
It  is  an  undoubted  fact  that  the  environment  has 
a very  decided  effect  upon  the  machine.  These 
direct  effects  of  the  environment  are  very  positive 
and  in  great  variety.  The  tropical  sun  darkens 
the  human  skin  ; cold  climate  stunts  the  growth 
of  plants;  lack  of  food  dwarfs  all  animals  and 
plants,  and  hundreds  of  other  similar  examples 
could  be  selected.  Another  class  of  similar  in- 
fluences are  those  produced  by  use  and  disuse . 
Beyond  question  the  use  of  an  organ  tends  to 
increase  its  size,  and  disuse  to  decrease  it.  Com- 
bats of  animals  with  each  other  tend  to  increase 
their  strength,  flight  from  enemies  their  running 
powers,  etc. 

Now  all  these  effects  are  direct  modifications 
of  the  machine,  and  if  they  are  only  transmitted 
to  following  generations  so  as  to  become  perma- 
nent modifications,  they  will  be  most  important 
agencies  in  the  machine  building.  If,  on  the 
other  hand,  they  are  not  transmitted  by  heredity, 
they  can  have  no  permanent  effect.  We  have 
here  thus  again  the  problem  of  the  inheritance 
of  acquired  characters,  We  have  already  noticed 


172  THE  STORY  OF  THE  LIVING  MACHINE. 

the  uncertainty  surrounding  this  subject,  but  the 
almost  universal  belief  in  the  inheritance  of  such 
characters  requires  ns  to  refer  to  it  again.  It  is 
uncertain  whether  such  direct  effects  have  any  in- 
fluence upon  the  offspring,  and  therefore  whether 
they  have  anything  to  do  with  this  machine  build- 
ing. Still,  there  are  many  facts  which  point 
strongly  in  this  direction.  For  example,  as  we 
study  the  history  of  the  horse  family  we  find  that 
an  originally  five-toed  animal  began  to  walk 
more  and  more  on  its  middle  toe,  in  su.ch  a way 
that  this  toe  received  more  and  more  use,  while 
the  outer  toes  were  used  less  and  less.  Now  that 
such  a habit  would  produce  an  effect  upon  the 
toes  in  any  generation  is  evident  ; but  apparently 
this  influence  extended  from  generation  to  gen- 
eration, for,  as  the  history  of  the  animals  is 
followed,  it  is  found  that  the  outer  toes  became 
smaller  and  smaller  with  the  lapse  of  ages,  while 
the  middle  one  became  correspondingly  larger, 
until  there  was  finally  produced  the  horse  with  its 
one  toe  only  on  each  foot.  Now  here  is  a line 
of  descent  or  machine  building  in  the  direct  line 
of  the  effects  of  use  and  disuse,  and  it  seems  very 
natural  to  suppose  that  the  modification  has  been 
produced  by  the  direct  effect  of  the  use  of  the 
organs.  There  are  many  other  similar  instances 
where  the  line  of  machine  building  has  been  quite 
parallel  to  the  effects  of  use  and  disuse.  If,  there- 
fore, acquired  characters  can  be  inherited  to  any 
extent,  we  have,  in  the  direct  influences  of  the 
environment  an  important  agency  in  machine 
building.  This  direct  effect  of  the  conditions 
is  apparently  so  manifest  that  one  school  of 
biologists  finds  in  it  the  chief  cause  of  the  varia- 
tions which  occur,  telling  us  that  the  conditions 


THE  LIVING  MACHINE  BUILDING  FACTORS.  173 

surrounding  the  organism  produce  changes  in  it, 
and  that  these  variations,  being  handed  down  to 
subsequent  generations,  constitute  the  basis  of 
the  development  of  the  machine.  If  this  factor 
is  entirely  excluded,  we  are  driven  back  upon  the 
natural  selection  of  congenital  variations  as  the 
only  kind  of  variations  which  can  permanently 
effect  the  modification  of  the  machine. 

Consciousness. — It  may  be  well  here  to  refer  to 
one  other  factor  in  the  problem,  because  it  has 
somewhat  recently  been  brought  into  prominence. 
This  factor  is  consciousness  on  the  part  of  the 
animal.  Among  plants  and  the  lower  animals 
this  factor  can  have  no  significance,  but  conscious- 
ness certainly  occurs  among  the  higher  animals. 
Just  when  or  how  it  appeared  are  questions  which 
are  not  answered,  and  perhaps  never  will  be.  But 
consciousness,  after  it  had  once  made  its  appear- 
ance, became  a controlling  factor  in  the  devel- 
opmentof  the  machine.  It  must  not  be  understood 
by  this  that  animals  have  had  any  consciousness 
of  the  development  of  their  body,  or  that  they 
have  made  any  conscious  endeavours  to  modify  its 
development.  This  has  not  always  been  under- 
stood. It  has  been  frequently  supposed  that  the 
claim  that  consciousness  has  an  influence  upon  the 
development  of  an  animal  means  that  the  animal 
has  made  conscious  efforts  to  develop  in  certain 
directions.  For  example,  it  has  been  suggested 
that  the  tiger,  conscious  of  the  advantage  of  being 
striped,  had  a desire  to  possess  stripes,  and  the 
desire  caused  their  appearance.  This  is  absurd. 
Consciousness  has  been  a factor  in  the  development 
of  the  machine,  but  an  indirect  one.  Conscious- 
ness leads  to  effort,  and  effort  has  a direct  influ- 
ence in  development.  For  example,  an  animal  is 


174  THE  story  of  the  living  machine. 

conscious  of  hunger,  and  this  leads  to  efforts  on 
his  part  to  obtain  food.  His  efforts  to  obtain 
food  may  lead, to  migration  or  to  the  adoption  of 
new  kinds  of  food  or  to  conflicts  with  various 
kinds  of  rivals,  and  all  of  these  efforts  are  potent 
factors  in  determining  the  direction  of  develop- 
ment. Consciousness,  again,  may  lead  certain 
animals  to  take  pleasure  in  each  other’s  society, 
or  to  recognize  that  in  mutual  association  they 
have  protection  against  common  enemies.  Such 
a consciousness  will  give  rise  to  social  habits,  and 
social  habits  are  a very  potent  factor  in  determin- 
ing the  direction  in  which  the  inherited  variations 
will  tend ; not,  perhaps,  because  it  effects  the  vari- 
ations themselves,  but  rather  because  it  deter- 
mines which  variations  among  the  many  shall  be 
preserved  and  which  rejected  by  natural  selec- 
tion. Consciousness  may  lead  the  antelope  to 
recognize  that  he  has  no  chance  in  a combat  with  a 
lion,  and  this  will  induce  him  to  flee.  The  habit  oi 
flight  would  then  develop  the  power  of  flight,  not 
because  the  antelope  desired  such  power,  but 
because  the  animals  with  variations  which  gave 
increased  power  of  flight  would  be  the  ones  to 
escape  the  lion,  while  the  slower  ones  would  die 
without  offspring.  Thus  consciousness  would 
indirectly,  though  not  directly,  result  in  the  length- 
ening of  the  legs  of  the  animal  and  in  the  strength- 
ening of  his  running  muscles.  Beyond  a doubt 
this  factor  of  consciousness  has  been  a factor  of 
no  little  moment  in  the  development  of  the  higher 
types  of  organic  machines.  We  can  as  yet  only 
dimly  understand  its  action,  but  it  must  hereafter 
be  counted  as  one  of  the  influences  in  the  evolu- 
tion of  the  living  machine. 

But,  after  all,  these  are  only  questions  of  the 


THE  LIVING  MACHINE  BUILDING  FACTORS.  175 

method  of  the  action  of  certain  well  demonstrated, 
fundamental  factors.  Whether  by  natural  selection, 
or  by  the  inheritance  of  acquired  characters  pro- 
duced by  the  environment,  or  whether  by  the  effect 
of  isolation  of  groups  of  individuals,  the  machine 
building  has  always  been  produced  in  the  same 
way.  A machine,  either  through  the  direct  influence 
of  the  environment,  or  as  a result  of  sexual  combi- 
nation of  germ  plasm,  shows  a variation  from  its 
parents.  This  variation  proves  of  value  to  its 
possessor,  who  lives  and  transmits  it  permanently 
to  posterity.  Thus  step  by  step,  one  part  is  add- 
ed to  another,  until  the  machine  has  grown  into 
the  intricately  adapted  structure  which  we  call  the 
animal  or  plant.  This  has  been  nature’s  method 
of  building  machines,  all  based  upon  the  three 
properties  possessed  by  the  living  cell — repro- 
duction, variation,  and  heredity. 

Summary  of  Nature’s  Power  of  Building  Ma- 
chines.— Let  us  now  notice  the  position  we  have 
reached.  Our  problem  in  the  present  chapter  has 
been  to  find  out  whether  nature'  possesses  forces 
adequate  to  explain  the  building  of  machines  with 
their  parts  accurately  adapted  to  each  other  so  as 
to  act  harmoniously  for  certain  ends.  Astronomy 
has  shown  that  she  has  forces  for  the  building  of 
worlds;  geology,  that  she  has  forces  for  making 
mountain  and  valley  ; and  chemistry,  that  she  has 
forces  for  building  chemical  compounds.  But  the 
organism  is  neither  a world,  nor  a mass  of  matter, 
nor  a chemical  compound.  It  is  a machine.  Has 
nature  any  forces  for  machine  building  ? We  have 
found  that  by  the  use  of  the  three  factors,  repro- 
duction, variation,  and  heredity,  nature  is  able  to 
produce  a machine  of  ever  greater  and  greater 
complexity,  with  the  parts  all  adapted  to  each 


176  THE  STORY  OF  THE  LIVING  MACHINE. 


other.  Now  the  difference  between  a machine 
and  a mass  of  matter  is  simply  in  the  adaptation 
of  parts  to  act  harmoniously  for  definite  ends. 
Hence  if  we  are  allowed  these  three  factors,  we 
can  say  that  nature  does  possess  forces  adequate  to 
the  manufacture  of  machines.  These  forces  are  not 
chemical  forces,  and  the  construction  of  the  ma- 
chine has  thus  been  brought  about  by  forces  en- 
tirely different  from  those  which  produced  the 
chemical  molecule. 

But  we  have  plainly  not  reached  the  bottom 
of  the  matter  in  our  attempt  to  explain  the  ma- 
chinery of  living  things.  We  have  based  the 
whole  process  upon  three  factors.  Reproduction, 
variation,  and  heredity  are  the  properties  of  all 
living  matter;  but  they  are  not,  like  gravity  and 
chemism,  universal  forces  of  nature.  They  oc- 
cur in  living  organisms  only.  Why  should  they 
occur  in  living  organisms,  and  here  alone  ? These 
three  properties  are  perhaps  the  most  marvellous 
properties  of  nature;  and  surely  we  have  not  fin- 
ished our  task  if  we  have  based  the  whole  process 
of  machine  building  upon  these  mysterious  phe- 
nomena, leaving  them  unintelligible.  We  must 
therefore  now  ask  whether  we  can  proceed  any 
farther  and  find  any  explanation  of  these  funda- 
mental powers  of  the  living  machine. 

It  must  be  confessed  that  here  we  are  at  present 
forced  to  stop.  We  can  proceed  no  further  with  any 
certainty,  or  even  probability.  We  may  say  that 
variation  and  heredity  are  only  phases  of  repro- 
duction, and  reproduction  is  a property  of  the  liv- 
ing cell.  We  may  say  that  this  power  of  repro- 
duction is  dependent  upon  the  power  of  assimila- 
tion and  growth,  for  cell  division  is  a result  of 
cell  growth.  We  may  further  say  that  growth 


THE  LIVING  MACHINE  BUILDING  FACTORS.  1 77 

and  assimilation  are  chemical  processes  resulting 
from  the  oxidation  of  food,  and  that  thus  all  of 
these  processes  are  to  be  reduced  to  chemical 
forces.  In  this  way  we  may  seem  to  have  a 
chemical  foundation  for  life  phenomena.  But 
clearly  this  is  far  from  satisfactory.  In  the  first 
place,  it  utterly  fails  to  explain  why  the  living  cell 
has  these  properties,  while  no  other  body  possesses 
them,  nor  why  they  are  possessed  by  living  pro- 
toplasms alone , ceasing  instantly  with  death.  In- 
deed it  does  not  tell  us  what  death  can  be.  Sec- 
ondly, it  utterly  fails  to  explain  the  marvels  of 
cell  division  with  resulting  hereditary  transmis- 
sion. For  all  this  we  must  fall  back  upon  the 
structure  of  protoplasm,  and  say  that  the  cell  ma- 
chinery is  so  adjusted  that  the  machine,  when 
acting  as  a whole,  is  capable  of  transforming  the 
energy  of  chemical  composition  in  certain  direc- 
tions. These  fundamental  properties  are  then  the 
properties  of  the  cell  machine  just  as  surely  as 
printing  is  The  property  of  the  printing  press. 
We  can  no  more  account  for  the  life  phenomena 
by  chemical  powers  than  we  can  for  printing  by 
chemical  forces  manifested  in  the  burning  of  the 
coal  in  the  engine  room.  To  be  sure,  it  is  the 
chemical  forces  in  the  engine  room  that  furnishes 
the  energy,  but  it  is  the  machinery  of  the  press 
that  explains  the  printing.  So,  while  chemical 
forces  supply  life  energy,  it  is  the  cell  machinery 
that  must  explain  the  fundamental  living  factors. 
So  long  as  this  machine  is  intact  it  can  continue 
to  run  and  perform  its  duties.  But  it  is  a very 
delicate  machine  and  is  easily  broken.  When  it 
is  broken  its  activities  cease.  A broken  machine 
can  not  run.  It  is  dead.  In  short,  we  come  back 
once  more  to  the  idea  of  the  machinery  of  pro- 


17 8 THE  STORY  OF  THE  LIVING  MACHINE. 

toplasm,  and  must  base  our  understanding  of  its 
properties  upon  its  structure. 

It  is  proper  to  state  that  there  are  still  some 
biologists  who  insist  that  the  ultimate  explanation 
of  protoplasm  is  purely  chemical  and  that  life  phe- 
nomena may  be  manifested  in  mixtures  of  com- 
pounds that  are  purely  physical  mixtures  and  not 
machines.  It  is  claimed  that  much  of  this  cell 
structure  described  above  is  due  to  imperfection 
in  microscopic  methods  and  does  not  really  exist 
in  living  protoplasm,  while  the  marvellous  activi- 
ties described  are  found  only  in  the  highly  organ- 
ized cell,  but  do  not  belong  to  simple  protoplasm. 
It  is  claimed  that  simple  protoplasm  consists  of  a 
physical  mixture  of  two  different  compounds 
which  form  a foam  when  thus  mixed,  and  that 
much  of  the  described  structure  of  protoplasm  is 
only  the  appearance  of  this  foam.  This  concep- 
tion is  certainly  not  the  prevalent  one  to-day ; and 
even  if  it  should  be  the  proper  one,  it  would  still 
leave  the  cell  as  an  extremely  complicated  ma- 
chine. Under  any  view  the  cell  is  a mechanism 
and  must  be  resolved  into  subordinate  parts. 
It  may  be  uncertain  whether  these  subordinate 
parts  are  to  be  regarded  simply  as  chemical  com- 
pounds physically  mixed,  or  as  smaller  units  each 
of  which  is  a smaller  mechanism.  At  all  events, 
at  the  present  time  we  know  of  no  such  simple 
protoplasm  capable  of  living  activities  apart  from 
machinery,  and  the  problem  of  explaining  life, 
even  in  the  simplest  form  known,  remains  the 
problem  of  explaining  a mechanism. 

The  Origin  of  the  Cell  Machine. — We  have  thus 
set  before  us  another  problem,  which  is  after  all 
the  fundamental  one,  namely,  to  ask  whether 
we  can  tell  anything  of  nature’s  method  of  build- 


THE  LIVING  MACHINE  BUILDING  FACTORS.  179 

ing  the  protoplasmic  machine.  The  building  of 
the  higher  animal  and  plant,  as  we  have  seen,  is 
the  result  of  the  powers  of  protoplasm;  but  proto- 
plasm itself  is  a machine.  What  has  been  its  his- 
tory ? 

We  must  first  notice  that  no  notion  of  chemical 
evolution  helps  us  out.  It  has  been  a favourite 
thought  with  some  that  the  origin  of  the  first  living 
thing  was  the  result  of  chemical  evolution.  As  the 
result  of  physical  forces  there  was  produced,  from 
the  original  nebulous  mass,  a more  and  more 
complicated  system  until  the  world  was  formed. 
Then  chemical  phenomena  became  more  and  more 
complicated  until,  with  the  production  of  more 
and  more  complicated  compounds,  protoplasm  was 
finally  produced.  A few  years  ago,  under  the  im- 
pulse of  the  idea  that  protoplasm  was  a com- 
pound, or  at  least  a simple  mixture  of  compounds, 
this  thought  of  protoplasm  as  the  result  of  chem- 
ical evolution  was  quite  significant.  Physical 
forces , chemical  forces,  and  vital  forces , explain  suc- 
cessively the  origin  of  worlds,  protoplasm , and  or- 
ganisms. This  conception  has,  however,  no  longer 
much  significance.  We  know  of  no  such  living 
chemical  compound  apart  from  cell  machinery. 
A new  conception  of  protoplasm  has  arisen  which 
demands  a different  explanation  of  its  origin. 
Since  it  is  a machine  rather  than  a compound, 
mechanical  rather  than  chemical  forces  are  re- 
quired for  its  explanation. 

Have  we  then  any  suggestion  as  to  the  method 
of  the  origin  of  this  protoplasmic  machine  ? Our 
answer  must,  at  the  present,  be  certainly  in  the 
negative.  The  complexity  of  the  cell  tells  us 
plainly  that  it  cannot  be  the  ultimate  living  sub- 
stance which  may  have  arisen  from  chemical  evo- 


180  THE  STORY  OF  THE  LIVING  MACHINE. 

lution.  It  is  made  up  of  parts  delicately  adapted 
to  act  in  harmony  with  each  other,  and  its  activity 
depends  upon  the  relation  of  these  parts.  What- 
ever chemical  forces  may  have  accomplished, 
they  never  could  have  combined  different  bodies 
into  linin,  centrosomes,  chromosomes,  etc.,  which, 
as  we  have  seen,  are  the  basis  of  cell  life.  To 
account  for  this  machine,  therefore,  we  are 
driven  to  assume  either  that  it  was  produced  by 
some  unknown  intelligent  power  in  its  present 
condition  of  complex  adjustment,  or  to  assume 
that  it  has  had  a long  history  of  building  by  suc- 
cessive steps,  just  as  we  have  seen  to  be  the  case 
with  the  higher  organisms.  The  latter  assump- 
tion is,  of  course,  in  harmony  with  the  general 
trend  of  thought.  To-day  protoplasm  is  produced 
only  from  other  protoplasm  ; but,  plainly,  the  first 
protoplasm  on  the  earth  must  have  had  a dif- 
ferent origin.  We  must  therefore  next  look  for 
facts  which  will  enable  us  to  understand  its  origin. 
We  have  seen  that  the  animal  and  plant  machines 
have  been  built  up  from  the  simple  cell  as  the 
result  of  its  powers  acting  under  the  ordinary 
conditions  of  nature.  Now,  in  accordance  with 
this  general  line  of  thought,  we  shall  be  compelled 
to  assume  that  previous  to  the  period  of  building 
machinery  which  we  have  been  considering,  there 
was  another  period  of  machine  building  during 
which  this  cell  machine  was  built  by  certain  natu- 
ral forces. 

But  here  we  are  forced  to  stop,  for  nothing 
which  we  yet  know  gives  even  a hint  as  to  the 
method  by  which  this  machine  was  produced. 
We  have,  however,  seen  that  there  are  forces  in 
nature  efficient  in  building  machines,  as  well  as 
those  for  producing  chemical  compounds  ; and  this, 


THE  LIVING  MACHINE  BUILDING  FACTORS.  181 

doubtless,  suggests  to  us  that  there  may  be  simi- 
lar forces  at  work  in  building  protoplasm.  If  we 
can  find  natural  forces  by  which  the  simplest  bit 
of  living  matter  can  be  built  up  into  a complicated 
machine  like  the  ox,  with  its  many  delicately  ad- 
justed parts,  it  is  certainly  natural  to  imagine 
that  the  same  forces  may  have  built  this  simpler 
machine  with  which  we  started.  But  such  a con- 
clusion is  for  a simple  reason  impossible.  We 
have  seen  that  the  essential  factor  in  this  machine 
building  is  reproduction,  with  the  correlated 
powers  of  variation  and  heredity.  Without  these 
forces  we  could  not  have  advanced  in  this  ma- 
chine building  at  all.  But  these  properties  are 
themselves  the  result  of  the  machinery  of  proto- 
plasm. We  have  no  reason  for  thinking  that  this 
property  of  reproduction  can  occur  in  any  other 
object  in  nature  except  this  protoplasmic  machine. 
Of  course,  then,  if  reproduction  is  the  result  of  the 
structure  of  protoplasm  we  can  not  use  this  factor 
in  explaining  the  origin  of  this  protoplasm.  The 
powers  of  the  completed  machine  can  not  be 
brought  forward  to  account  for  its  origin.  Thus 
the  one  fundamental  factor  for  machine  building 
is  lacking,  and  if  we  are  to  explain  nature’s 
method  of  producing  protoplasm  from  simpler 
structures,  we  must  either  suppose  that  the  parts 
of  the  cell  are  capable  of  reproduction  and  subject 
to  heredity,  or  we  must  look  for  some  other  method. 
Such  a road  has  however  not  yet  been  found,  nor 
have  we  any  idea  in  what  direction  to  look. 
But  the  fact  that  nature  has  methods  of  machine 
building,  as  we  have  seen,  may  hold  out  the  pos- 
sibility that  some  day  we  may  discover  her 
method  of  building  this  primitive  living  machine, 
the  cell. 


1 82  THE  STORY  OF  THE  LIVING  MACHINE. 

It  is  useless  to  try  to  go  further  at  pres- 
ent. The  origin  of  living  matter  is  shrouded  in 
as  great  obscurity  as  ever.  We  must  admit  that 
the  disclosures  of  the  modern  microscope  have 
complicated  rather  than  simplified  this  problem. 
While  a few  years  ago  chemists  and  biologists 
were  eagerly  expecting  to  discover  a method  of 
manufacturing  a bit  of  living  matter  by  artificial 
means,  that  hope  has  now  been  practically  aban- 
doned. The  task  is  apparently  hopeless.  We  can 
manipulate  chemical  forces  and  produce  an  end- 
less series  of  chemical  compounds.  But  we  can 
not  manipulate  the  minute  bits  of  matter  which 
make  up  the  living  machine.  Since  living  matter 
is  made  of  the  adjustment  of  these  microscopic 
parts  of  matter,  we  can  not  hope  to  make  a bit 
of  living  matter  until  we  find  some  way  of  making 
these  little  parts  and  adjusting  them  together. 
Most  students  of  protoplasm  have  therefore 
abandoned  all  expectation  of  making  even  the 
simplest  living  thing.  We  are  apparently  as  far 
from  the  real  goal  of  a natural  explanation  of  life 
as  we  were  before  the  discovery  of  protoplasm. 

General  Summary. — It  is  now  desirable  to  close 
this  discussion  of  seemingly  somewhat  uncon- 
nected topics  by  bringing  them  together  in  a brief 
summary.  This  will  enable  us  to  see  more 
clearly  the  position  in  which  science  stands  to-day 
upon  this  matter  of  the  natural  explanation  of 
living  phenomena,  and  to  picture  to  ourselves 
more  concisely  our  knowledge  of  the  living 
machine. 

The  problem  we  have  set  before  us  is  to  find 
out  to  what  extent  it  is  possible  to  account  for 
vital  phenomena  by  the  application  of  ordinary 
natural  laws  and  forces,  and  therefore  to  find  out 


THE  LIVING  MACHINE  BUILDING  FACTORS.  I S3 

whether  it  is  necessary  to  assume  that  there  are 
forces  needed  to  explain  life  which  are  different 
from  those  found  in  other  realms  of  nature,  or 
whether  vital  forces  are  all  correlated  with  physi- 
cal forces.  It  has  been  evident  at  a glance  that 
the  living  body  is  a machine.  Like  other  ma- 
chines it  consists  of  parts  adjusted  to  each  other 
for  the  accomplishment  of  definite  ends,  and  its 
action  depends  upon  the  adjustment  of  its  parts. 
Like  other  machines,  it  neither  creates  nor  de- 
stroys energy,  but  simply  converts  the  potential 
energy  of  its  foods  into  some  form  of  active 
energy,  and,  like  other  machines,  its  power  ceases 
when  the  machine  is  broken. 

With  this  understanding  the  problem  clearly 
resolved  itself  into  two  separate  ones.  The  first 
was  to  determine  to  what  extent  known  physical 
and  chemical  laws  and  forces  are  adequate  to  an 
explanation  of  the  various  phenomena  of  life 
The  second  was  to  determine  whether  there  are 
any  known  forces  which  can  furnish  a natural 
explanation  of  the  origin  of  the  living  machine. 
Manifestly,  if  the  first  of  these  problems  is  insolv- 
able,  the  second  is  insolvable  also. 

In  the  study  of  the  first  problem  we  have 
reached  the  general  conclusion  that  the  secondary 
phenomena  of  life  are  readily  explained  by  the 
application  of  physical  and  chemical  forces  act- 
ing in  the  living  machine.  These  secondary  phe- 
nomena include  such  processes  as  the  digestion 
and  absorption  of  food,  circulation,  respiration, 
excretion,  bodily  motion,  etc.  Nervous  phenom- 
ena also  doubtless  come  under  this  head,  at  least 
so  far  as  concerns  nervous  force.  We  have  been 
obliged,  however,  to  exclude  from  this  correlation 
the  mental  phenomena.-  Mental  phenomena  can 

13 


184  THE  STORY  OF  THE  LIVING  MACHINE. 

not  as  yet  be  measured,  and  have  not  yet  been 
shown  to  be  correlated  with  physical  energy.  In 
other  words,  it  has  not  yet  been  proved  that 
mental  force  is  energy  at  all ; and  if  it  is  not 
energy,  then  of  course  it  can  not  be  included  in 
.the  laws  which  govern  the  physical  energy  of 
the  universe.  Although  a close  relation  exists 
between  physical  changes  in  the  brain  cells  and 
mental  phenomena,  no  further  connection  has  yet 
been  drawn  between  mental  power  and  physical 
force.  All  other  secondary  phenomena,  however, 
are  intelligently  explained  by  the  action  of  natu- 
ral forces  in  the  machinery  of  the  living  organ- 
ism. 

While  we  have  thus  found  that  the  secondary 
phenomena  of  life  are  intelligible  as  the  result  of 
the  structure  of  the  machine,  certain  other  fun- 
damental phenomena  have  been  constantly  forc- 
ing themselves  upon  our  attention  as  a founda- 
tion of  these  secondary  activities.  The  power  of 
contraction,  the  power  of  causing  certain  kinds 
of  chemical  change  to  occur  which  result  in  me- 
tabolism, the  property  of  sensibility,  the  property 
of  reproduction — these  are  fundamental  to  all  liv- 
ing activity,  and  are,  after  all,  the  real  phenom- 
ena which  we  wish  to  explain.  Rut  these  are  not 
peculiar  to  the  complicated  machines.  We  can 
discard  all  the  apparent  machinery  of  the  animal 
or  plant  and  find  these  properties  still  developed 
in  the  simplest  bit  of  living  matter.  To  learn 
their  significance,  therefore,  we  have  turned  to 
the  study  of  the  simplest  form  of  matter  in  which 
these  fundamental  properties  are  manifested. 
This  led  us  at  once  to  the  study  of  the  so-called 
protoplasm,  for  protoplasm  is  the  simplest  known 
form  of  matter  that  is  alive.  Protoplasm  itself 


THE  LIVING  MACHINE  BUILDING  FACTORS.  185 

at  first  seemed  to  be  a homogeneous  body,  and 
was  looked  upon  as  a chemical  compound  of 
high  complexity.  If  this  were  true  its  properties 
would  depend  upon  its  composition  and  would  be 
explained  by  the  action  of  chemical  forces.  Such 
a conception  would  have  quickly  solved  the  prob- 
lem, for  it  would  reduce  living  properties  to 
chemical  powers.  But  the  conception  proved  to 
be  delusive.  Protoplasm,  at  least  the  simplest 
form  known  to  possess  the  fundamental  life  prop- 
erties, soon  showed  itself  to  be  no  chemical  com- 
pound, but  a machine  of  wonderful  intricacy. 

The  fundamental  phenomena  of  life  and  of 
protoplasm  have  proved  to  be  both  chemical  and 
mechanical.  Metabolism  is  the  result  of  the 
oxidation  of  food,  and  motion  is  an  instance  of 
transference  of  force.  Our  problem  then  re- 
solved itself  into  finding  the  power  that  guides 
the  action  of  these  natural  forces.  Food  will 
not  undergo  such  an  oxidation  except  in  the 
presence  of  protoplasm,  nor  will  the  phenomena  of 
metabolism  occur  except  in  the  presence  of  living 
protoplasm.  Clearly,  then,  the  living  protoplasm 
contains  within  itself  the  power  of  guiding  this 
play  of  chemical  force  in  such  a way  as  to  give 
rise  to  vital  phenomena,  and  our  search  must  be 
not  for  chemical  force  but  for  this  guiding  prin- 
ciple. Our  study  of  protoplasm  has  told  us 
clearly  enough  that  we  must  find  this  guiding 
principle  in  the  interaction  of  the  machinery 
within  the  protoplasm.  The  microscope  has  told 
us  plainly  that  these  fundamental  principles  are 
based  upon  machinery.  The  cell  division  (repro- 
duction) is  apparently  controlled  by  the  centro- 
some;  the  heredity  by  the  chromosomes;  the  con- 
structive metabolism  by  the  nucleus  in  general, 


1 86  THE  STORY  OF  THE  LIVING  MACHINE. 

while  the  destructive  metabolism  is  also  seated  in 
the  cell  substance  outside  the  nucleus.  Whether 
these  statements  are  strictly  accurate  in  detail 
does  not  particularly  affect  the  general  conclu- 
sion. It  is  clearly  enough  demonstrated  that  the 
activities  of  the  protoplasmic  body  are  dependent 
upon  the  relation  of  its  different  parts.  Although 
we  have  got  rid  of  the  complicated  machinery 
of  the  organism  in  general,  we  are  still  confronted 
with  the  machinery  of  the  cell. 

But  our  analysis  can  not,  at  present,  go  further. 
Our  knowledge  of  this  machine  has  not  as  yet 
enabled  us  to  gain  any  insight  as  to  its  method 
of  action.  We  can  not  yet  conceive  how  this  ma- 
chine controls  the  chemical  and  physical  forces 
at  its  disposal  in  such  a way  as  to  produce  the 
orderly  result  of  life.  The  strict  correlation  be- 
tween the  forces  of  the  physical  universe  and 
those  manifested  by  this  protoplasm  tells  us  that 
a transformation  of  energy  occurs  within  it,  but 
of  the  method  of  that  transformation  we  as  yet 
know  nothing.  Irritability,  movement,  metabo- 
lism, and  reproduction  appear  to  be  not  chemical 
properties  of  a compound,  but  mechanical  prop- 
erties of  a machine.  Our  mechanical  analysis  of 
the  living  machine  stops  short  before  it  reaches 
any  foundation  in  the  chemical  forces  of  nature. 

It  is  thus  clearly  apparent  that  the  phenomena 
of  life  are  dependent  upon  the  machinery  of  liv- 
ing things,  and  we  have  therefore  the  second 
question  of  the  origin  of  this  machinery  to 
answer.  Chemical  forces  and  mechanical  forces 
have  been  laboriously  investigated,  but  neither 
appear  adequate  to  the  manufacture  of  machines. 
They  produce  only  chemical  compounds  and 
worlds  with  their  mountains  and  seas.  The  con- 


THE  LIVING  MACHINE  BUILDING  FACTORS.  187 

struction  of  artificial  machines  has  demanded  in- 
telligence. But  here  is  a natural  machine — the 
organism.  It  is  the  only  machine  produced  by 
natural  methods,  so  far  as  we  know  ; and  we  have 
therefore  next  asked  whether  there  are,  in  nature, 
simple  forces  competent  to  build  machines  such 
as  living  animals  and  plants  ? 

In  pursuance  of  this  question  we  have  found 
that  the  complicated  machines  have  been  built 
out  of  the  simpler  ones  by  the  action  of  known 
forces  and  laws.  The  factors  in  this  machine 
building  are  simply  those  of  the  fundamental  vital 
properties  of  the  simplest  protoplasmic  machine. 
Reproduction,  heredity,  and  variation,  acting 
under  the  ever-changing  conditions  of  the  earth’s 
surface,  are  apparently  all  that  are  needed  to  ex- 
plain the  building  of  the  complex  machines  out  of 
the  simpler  ones.  Nature  has  forces  adequate  to 
the  building  of  machines  as  well  as  forces  ade- 
quate to  the  formation  of  chemical  compounds 
and  worlds. 

But  here  again  we  are  unable  to  base  our  ex- 
planation upon  chemical  and  physical  forces. 
Reproduction,  heredity,  and  variation  are  prop- 
erties of  the  cell  machine,  and  we  are  therefore 
thrown  back  upon  the  necessity  of  explaining  the 
origin  of  this  machine.  Can  we  find  a mechanical 
or  chemical  explanation  of  the  origin  of  proto- 
plasm ? A chemical  explanation  of  the  cell  is  im- 
possible, since  it  is  not  a chemical  compound,  but 
a piece  of  mechanism.  The  explanation  given 
for  the  origin  of  animals  and  plants  is  also  here 
apparently  impossible.  The  factors  upon  which 
that  explanation  depended  are  factors  of  this 
completed  machine  itself,  and  can  not  be  used  to 
explain  its  origin.  We  are  left  at  present  there-^ 


1 88  THE  STORY  OF  THE  LIVING  MACHINE. 

fore  without  any  foundation  for  further  advance. 
The  cells  must  have  had  a history  of  construc- 
tion, but  we  do  not  as  yet  conceive  any  forces 
which  may  be  looked  upon  as  contributing  to 
that  history.  Whether  life  phenomena  can  be 
manifested  by  any  mixture  of  compounds  simpler 
than  the  cell  we  do  not  yet  know. 

The  great  problems  still  remaining  for  solu- 
tion, which  have  hardly  been  touched  by  modern 
biology  in  all  its  endeavours  to  find  a mechanical 
explanation  of  the  living  machine,  are,  therefore, 
three.  First,  the  relation  of  mentality  to  the 
general  phenomena  of  the  correlation  of  force; 
second,  the  intelligible  understanding  of  the 
mechanism  of  protoplasm  which  enables  it  to 
guide  the  blind  chemical  and  physical  forces  of 
nature  so  as  to  produce  definite  results;  third, 
the  kind  of  forces  which  may  have  contributed 
to  the  origin  of  that  simplest  living  machine  upon 
whose  activities  all  vital  phenomena  rest — the 
living  cell. 


INDEX 


A. 

Absorption  of  food,  29. 

Acquired  characters,  inheritance  of, 
164,  165,  166,  167,  171. 

variations,  159,  160. 

Amoeba,  73. 

Anatomical  evidence  for  evolution, 
142. 

Aquacity,  80. 

Arm  compared  with  wing,  144. 
Aristotle,  1. 

Assimilation,  80,  124,  149,  176. 
Asters  of  dividing  cells,  98. 

B. 

Barry,  63,  64. 

Bathybias,  84. 

Biology  a new  science, #i,  5,  15. 
Blood,  35,  36,  38,  69,  73. 
Blood-vessels,  35,  36. 

Body  as  a machine,  22,  25,  49. 

Bone  cells,  69. 

Building  of  the  living  machine,  131, 
134,  136,  137,  167,  175,  180. 

C. 

Cartilage  cells,  68. 

Cell  as  a machine,  126,  128. 

description  of,  69. 

division,  95,  96,  101. 

discovery  of,  58. 

doctrine,  60. 

substance,  65,  125. 

Cells,  56,  84,  86,  118,  119. 

Cellular  structure  of  organisms,  65. 
Cell  wall,  64,  72. 

Centrosome,  94,  96,  97,  101,  103, 
105,  no. 

Challenger  expedition,  83, 


Chemical  evolution,  179. 

Chemical  theory  of  vitality,  14  ; of 
life,  78,  1 16. 

Chemism  or  mechanism,  57,  176. 

Chemistry  of  digestion,  27,  28  ; of 
protoplasm,  76  ; of  respiration,  38. 

Chromatin,  92,  94,  96,  102,  149,  153. 

Chromosomes,  97,  98,  101,  105,  108, 
no,  113,  152. 

Circulation,  34. 

Colonies  of  cells,  85. 

Comparison  of  the  body  and  a ma- 
chine, 22. 

Congenital  variations,  158,  160,  163  ; 
inheritance  of,  164. 

Connective-tissue  cells,  70. 

Conservation  of  energy,  7,  17. 

Consciousness  as  a factor  in  machine 
building,  173. 

Constructive  chemical  processes,  so. 
51,  52,  124. 

Continuity  of  germ  plasm,  155. 

Correlation  of  vital  and  physical 
forces,  13,  16,  22,  23,  24,  25. 

Cytoblastema.  62. 

Cytology,  10. 

D. 

Darwin,  8r. 

Death  of  the  cell,  127. 

Decline  of  the  reign  of  protoplasm, 
8S* 

Destructive  chemical  processes,  50, 
51,  52,  125. 

Dialysis,  29,  30,  31. 

Digestion,  27. 

E. 

Egg,  102,  120,  152. 

— — division  of,  63. 

189 


190  THE  STORY  OF  THE  LIVING  MACHINE. 


Egg,  fertilization  of,  102. 
Embrvological  evidence  for  evolu- 
tion, 140. 

Energy  of  nervous  impulse,  43,  54. 
Environment,  171. 

Evidence  for  evolution  as  a method 
of  machine  building,  139,  145. 
Evolution,  9,  16,  81,  134. 
Experiments  with  developing  eggs, 
121. 

F. 

Fat,  absorption  of,  32. 

Female  pronucleus,  no. 

Fern  cells,  section  of,  67. 
Fertilization  of  the  egg,  95,  102  ; 

significance  of,  112. 

Fibres  in  protoplasm,  87  ; in  spindle, 
98,  101. 

Forces  at  work  in  machine  building, 
148,  176,  181. 

Formed  material,  64. 

Free  cell  formation,  64. 

G. 

Geological  evidence  for  evolution, 
*39-  , 

Germ  plasm,  154. 

H. 

Heart  as  a pump,  35. 

Heat,  24,  44,  45. 

Heredity,  148,  150,  176 ; explana- 
tion of,  152. 

Hereditary  traits,  113,  153. 
Historical  geology,  6. 

History  of  the  living  machine,  133, 
147. 

Horses’  toes,  loss  of,  172. 

Huxley,  11,  75,  83,  84. 

I. 

Irritability,  54. 

Isolation,  theory  of,  170. 

K. 

Karyokinesis,  96,  101. 

Kidneys,  41. 

L. 

Leaf,  section  of,  66. 

Life  the  result  of  a mechanism,  115, 
177. 


Lin  in,  92,  103. 

Linnaeus,  1. 

Lyell,  6. 

Lymph,  36,  37. 

M. 

Machine  defined,  20. 

Machines  the  result  of  mechanical 
forces,  1 16. 

Male  cell,  104,  107. 

pronucleus,  109. 

Maturation  of  the  egg,  104. 
Mechanical  nature  of  living  organ- 
isms, 12. 

Mechanical  theory  of  life,  81,  144. 
Membrane  of  the  nucleus,  92,  101. 
Mental  phenomena,  47,  48. 
Metabolism,  54. 

Microsomes,  87. 

Migration,  theory  of,  170. 

Monera,  88. 

Movement,  54. 

Muscle,  36,  71. 

N. 

Natural  selection,  167. 

Nerve-fibre  cell,  70. 

Nervous  energy,  42,  44. 

system,  41. 

New  biological  problems,  15. 
Nucleolus,  65,  92,  94. 

Nucleus,  65,  84,  87,  93,  101,  103,  113, 
124,  149;  formation  of  new,  101. 

functiofi  of,  89,  90,  95. 

presence  of,  87,  88,  89. 

structure  of,  91. 

O. 

Organic  chemistry,  78. 

Organic  compounds,  artificial  man- 
ufacture of,  78,  82. 

Origin  of  cell  machine,  178,  179, 180. 
Ongin  of  life,  81,  182. 

Osmosis,  29. 

Oxidation,  80,  176. 

as  a vital  process,  39,  56. 

P. 

Philosophical  biology,  4. 

Physical  basis  of  life,  75. 

Polar  cells,  107. 

Potato,  section  of  cells,  67. 
Properties  of  chemical  compounds, 
79* 


INDEX. 


191 


Protoplasm,  14,  74,  82,  83,  84,  114, 

115,  179* 

artificial  manufacture  of,  82. 

as  a machine,  86,  178. 

discovery  of,  74. 

nature  of,  76. 

structure  of,  86,  87. 

Purpose  vs.  cause,  11,  12. 

R. 

Reaction  against  the  cell  doctrine, 

n7. 

Reign  of  law,  4. 

of  the  nucleus,  91. 

of  protoplasm,  81,  85. 

Relationship,  significance  of,  143. 
Removal  of  waste,  39,  40. 
Reproduction,  54,  bo,  124,  148,  176 ; 

rapidity  of,  149. 

Respiration,  37. 

Reticulum  of  cell,  87 ; of  nucleus, 
92  . 

Root  tip,  section  of,  66. 


S. 

Schultze,  74,  75. 

Schwann,  61,  62,  72. 
Secretion,  39,  40. 
Segmentation  nucleus,  no. 


Sensations,  46. 

Separation  of  chromosomes,  100. 
Sexual  reproduction,  102. 
Spermatozoan,  107,  109,  154. 
Splitting  of  chromosomes,  99. 
Spindle  fibres,  101. 

Struggle  for  existence,  168. 
Summary  of  Part  I,  128. 

general,  182. 

U. 

Undifferentiated  protoplasm,  83. 
Unicellular  animals,  71. 

Units  of  vital  activity,  53. 

Use  and  disuse,  171,  172. 

V. 

Variation,  148,  157,  160,  176. 
Variation  from  sexual  union,  162. 
Variation  in  germ  plasm,  161. 
Vegetative  functions,  41. 

Villi,  31. 

Vital  force,  vitality,  13,  15,  34,  37, 
52,  80,  85. 

Vital  properties,  54  ; located  in  cells, 
123. 

W. 

Wing  compared  with  arm,  144. 
Wood  cells,  68. 


(6) 


THE  END, 


THE  LIBRARY  OF  USEFUL  STORIES. 

Illustrated*  J6mo*  Cloth,  35  cents  net  per  volume; 
postage,  4 cents  per  volume  additional* 


The  Story  of  Extinct  Civilizations  of  the  West.  By 
Robert  E.  Anderson,  M.  A.,  F.  A.  S. 

The  Story  of  Alchemy.  By  M.  M.  Pattison  Muir. 
The  Story  of  Animal  Life.  By  B Lindsay. 

The  Story  of  the  Art  of  Music.  By  F.  J.  Crowest. 
The  Story  of  the  Art  of  Building.  By  P.  L.  Water- 
house. 

The  Story  of  King  Alfred.  By  Sir  Walter  Besant. 
The  Story  of  Books.  By  Gertrude  B.  Rawlings. 
The  Story  of  the  Alphabet.  By  Edward  Clodd. 

The  Story  of  Eclipses.  By  G.  F.  Chambers,  F.  R.  A.  S. 
The  Story  of  the  Living  Machine.  By  H.  W.  Conn. 
The  Story  of  the  British  Race.  By  John  Munro,  C.E. 
The  Story  of  Geographical  Discovery.  By  Joseph 
Jacobs. 

The  Story  of  the  Cotton  Plant.  By  F. Wilkinson,  F.G.S. 
The  Story  of  the  Mind.  By  Prof.  J.  Mark  Baldwin. 
The  Story  of  Photography.  By  Alfred  T.  Story. 
The  Story  of  Life  in  the  Seas.  By  Sydney  J.  Hickson. 
The  Story  of  Germ  Life.  By  Prof.  H.  W.  Conn. 

The  Story  of  the  Earth’s  Atmosphere.  By  Douglas 
Archibald. 

The  Story  of  Extinct  Civilizations  of  the  East.  By 
Robert  Anderson,  M.  A.,  F.  A.  S. 

The  Story  of  Electricity.  By  John  Munro,  C.  E. 

I The  Story  of  a Piece  of  Coal.  By  E.  A.  Martin,  F.G.S. 
The  Story  of  the  Solar  System.  By  G.  F.  Chambers. 
The  Story  of  the  Earth.  By  H.  G.  Seeley,  F.  R.S. 
The  Story  of  the  Plants.  By  Grant  Allen. 

The  Story  of  “ Primitive”  Man.  By  Edward  Clodd. 
The  Story  of  the  Stars.  By  G.  F.  Chambers,  F.  R.  A.  S. 

D.  APPLETON  AND  COMPANY,  NEW  YORK. 


APPLETONS*  NEW  PHYSIOLOGIES. 


First  Book  in  Hygiene. 

A Beautiful  Book  of  Health  for  the  Little  Folks. 
Price,  35  cents. 

Graded  Lessons  in  Hygiene. 

A Complete  Course  in  One  Book.  Price,  60 
cents. 

By  William  O.  Krohn,  Ph.D.,  Author  of  “ Prac- 
tical Lessons  in  Psychology  ; ” Editor  of  “ The 
Child  Study  Monthly,”  etc. 

In  this  new  series  of  text-books  on  Physiology  and  Hygiene  Dr. 
Krohn  has  recognized  and  supplied  the  need  for  simple,  clear,  and 
interesting  explanations  of  the  laws  and  safeguards  of  health  which 
grammar-school  children  may  easily  grasp  and  understand.  The 
chief  purpose  of  these  books  is  to  impress  upon  children  the  neces- 
sity for  right  living,  and  to  instruct  them  in  the  way  to  keep  strong. 
They  are  not  intended  to  be  text-books  of  Anatomy  or  Physiology, 
although  they  include  enough  information  about  these  branches  for 
a correct  knowledge  of  the  body’s  general  structure  and  the  most 
important  functions  of  its  principal  organs.  The  facts  given  are  in 
agreement  with  the  results  of  the  most  recent  scientific  investiga- 
tions, and  the  accuracy  of  the  statements  made  by  Dr.  Krohn  is 
attested  by  such  specialists  as  Dr.  William  T.  Sedgwick  and  Dr. 
Theodore  Hough,  of  the  Massachusetts  Institute  of  Technology. 

SOME  OPINIONS  FROM  EDUCATORS . 

“Your  ‘ First  Book  in  Hygiene  ’ is  a gem.” 

“ It  is  an  excellent  primer  of  physiology.” 

“A  charming  book.  Children  will  enjoy  it.” 

“Teachers  are  continually  asking  for  it.” 

“‘Graded  Lessons  in  Hygiene’  is  the  best  book  on  the  subject  I 
have  ever  read.” 

“The  selection  of  material  has  been  most  wisely  made.” 

“No  text-book  has  kept  so  close  to  essentials.” 

“ This  kind  of  school  book  is  much  needed.” 

We  should  be  pleased  to  inform  you  further  as  to  the  merits  of 
these  books.  Why  not  let  us  send  you  a copy  for  your  inspection  ? 


D.  APPLETON  AND  COMPANY, 

NEW  YORK.  BOSTON.  CHICAGO.  LONDON. 


NATURAL  PHILOSOPHY  IN  FOUR  VOLUMES. 


Elementary  Treatise  on  Natural  Philosophy. 

By  A.  Privat  Deschanel,  formerly  Professor  of  Physics 
in  the  Lycee  Louis-le-Grand,  Inspector  of  the  Academy  of 
Paris.  Translated  and  edited,  with  extensive  modifications, 
by  J.  D.  Everett,  Professor  of  Natural  Philosophy  in  the 
Queen’s  College,  Belfast.  Complete  in  Four  Parts.  Illus- 
trated by  783  Engravings  on  Wood  and  3 Colored  Plates. 
I.  Mechanics,  Hydrostatics,  and  Pneumatics.  8vo.  Cloth, 
$1.50.  II.  Heat.  8vo.  Cloth,  $1.50.  III.  Electricity  and 
Magnetism.  8vo.  Cloth,  $1.50.  IV.  Sound  and  Light.  8vo. 
Cloth,  $1.50.  Complete  in  1 vol.  8vo.  With  Problems  and 
Index.  Cloth,  $5.75.  In  the  latest  revised  edition. 

Electricity — Part  III  of  Everett’s  Deschanel — has  been 
expanded  on  the  lines  of  modern  electrical  theory.  Hence 
Part  III  forms  a new  and  thoroughly  modern  text-book  of 
electricity — the  need  for  which,  in  view  of  the  great  advance 
in  electrical  science,  has  been  long  apparent  to  every  teacher. 

u Systematically  arranged,  clearly  written,  and  admirably  illustrated, 
showing  no  less  than  760  engravings  on  wood  and  three  colored  plates,  it 
forms  a model  work  for  a class  of  experimental  physics.  Far  from  losing 
in  its  English  dress  any  of  the  qualities  of  matter  or  style  which  distin- 
guished it  in  its  original  form,  it  may  be  said  to  have  gained  in  the  able 
hands  of  Professor  Everett,  both  by  way  of  arrangement  and  of  incorpo- 
ration of  fresh  matter,  without  parting  in  the  translation  with  any  of  the 
freshness  or  force  of  the  author’s  text.” — Saturday  Review. 

“Electrical  theory  has  been  revolutionized,  . . . and  this  connected 
exposition  of  it  on  mathematical  lines,  without  demanding  exceptional 
mathematical  knowledge,  will  be  a boon  to  students  of  the  subject.  . . . 
New  chapters,  up  to  date,  are  given  on  the  following  subjects:  Electrical 
action  in  dielectrics ; the  transmission  of  signals  through  long  wires ; 
electro-magnetic  induction,  very  fully  treated  ; dynamos  and  electromo- 
tors, including  the  theory  of  a production  of  a rotating  field  by  polyphase 
currents ; modern  galvanometers  ; electro-chemistry  and  thermo-electric- 
ity. The  engravings  are  as  good  as  those  of  the  original  work  and  many 
have  been  added  from  Professors  Ayrton,  S.  P.  Thompson,  Ewing,  and 
Sir  W.  Preece.” — From  the  Educational  Times . 


D.  APPLETON  AND  COMPANY,  NEW  YORK. 


TWENTIETH  CENTURY  TEXTBOOKS  OF  SCIENCE. 


TEXT-BOOKS  OF  ZOOLOGY. 

By  David  Starr  Jordan,  Ph.  D.,  LL.  D.,  President  of 
Leland  Stanford  Junior  University  ; Vernon  L.  Kel- 
logg, M.  S.,  and  Harold  Heath,  Ph.  D.,  Professors 
in  Leland  Stanford  Junior  University. 

Animal  Studies. 

An  Elementary  Zoology.  $1.25. 

Animal  Life. 

A First  Book  of  Zoology.  $1.20. 

Animal  Forms. 

A Text-Book  of  Zoology.  $1.10. 

Animals. 

Animal  Life  and  Animal  Forms  in  one  volume.  $1.80. 
Animal  Structures. 

A Laboratory  Manual  of  Zoology.  By  D.  S.  Jordan  and 
George  C.  Price.  75  cents. 

An  Introduction  to  Physical  Geography. 

By  Grove  K.  Gilbert,  LL.  D.,  United  States  Geolog- 
ical Survey,  and  Albert  P.  Brigham,  Professor  of  Geology, 
Colgate  University.^  $1.25. 

A Text-Book  of  Geology. 

By  Albert  Perry  Brigham,  A.  M.  $1.40. 

An  Elementary  Chemistry. 

With  Experiments.  By  Robert  Hart  Bradbury, 
A.  M.,  Ph.  D.,  Teacher  of  Chemistry,  Central  Manual  Train- 
ing School,  Philadelphia.  $1.25.  Experiments  separately, 
45  cents. 

The  Elementary  Principles  of  Chemistry. 

By  Abram  Van  Eps  Young,  Ph.  B.,  Northwestern  Uni- 
versity, Evanston,  111.  95  cents.  With  Experiments,  $i.io. 

Laboratory  Experiments  separately,  45  cents. 

D.  APPLETON  AND  COMPANY,  NEW  YORK. 


By  WILLIAM  C*  EDGAR* 


The  Story  of  a Grain  of  Wheat. 

By  William  C.  Edgar,  Editor  of  “The  North- 
western Miller.”  Illustrated.  Cloth,  $1.00  net ; 
postage,  io  cents  additional. 

The  story  of  wheat  is  a marvelous  one,  and  is  here 
told  with  all  the  interest  of  a narrative.  A short  chapter 
dealing  with  the  character  of  the  berry  itself,  and  its  ene- 
mies, diseases,  and  pests,  precedes  its  earlier  history  from 
its  probable  birthplace  in  the  valley  of  the  Euphrates 
to  its*  cultivation  in  modern  times.  Then  follows  a re- 
view of  Britain’s  supplies  and  requirements,  with  a brief 
review  of  the  fields  of  France,  Germany,  and  other 
European  countries.  India  is  considered  as  a wheat 
producer,  and  Russia’s  ability  to  compete  in  the  world’s 
markets  is  discussed. 

This  book  will  merit  the  attention  of  the  general 
reader  who  may  not  be  practically  interested  in  wheat 
and  its  products,  because  of  its  direct  and  lucid  narra- 
tive, telling  the  story  which  appeals  to  all  human  kind — 
the  story  of  man’s  long-continued  struggle  for  plenty 
and  his  final  triumph  over  savagery  and  want.  Its 
special  and  exceptional  value,  however,  beyond  its  in- 
trinsic worth,  will  be  to  those  who  are  concerned  directly 
or  remotely  in  the  making  of  flour,  its  handling  and  sale, 
or  its  manufacture  into  bread.  By  these  it  will  be  wel- 
comed as  a book  of  record  and  reference,  an  exponent 
of  the  fundamental  principles  of  their  particular  industry 
and  an  impartial  history  of  its  achievements,  written  by 
one  who  is  in  full  sympathy  with  its  broader  and  higher 
aspirations. 


D.  APPLETON  AND  COMPANY,  NEW  YORK. 


A PRACTICAL,  COMMON-SENSE  MANUAL. 


The  Care  and  Feeding  of  Children. 

A Catechism  for  the  Use  of  Mothers  and 
Children’s  Nurses.  By  L.  Emmett  Holt,  M.D., 
LL.D.,  Professor  of  Diseases  of  Children  in  the 
New  York  Polyclinic,  Attending  Physician  to  the 
Babies’  Hospital  and  the  Nursery  and  Child’s 
Hospital,  New  York.  Third  edition,  revised  and 
enlarged.  i2mo.  Cloth,  75  cents  net  ; postage, 
7 cents  additional. 

Probably  no  book  ever  written  has  relieved  more  human 
suffering  or  actually  saved  more  little  lives  than  this  simple 
catechism  of  Dr.  Holt’s. 

Thousands  of  copies  have  found  their  way  into  homes  all  over 
the  land,  and  in  only  too  many  instances  have  the  words  and 
instruction  of  this  eminent  authority  revealed  a surprising  lack  of 
knowledge,  even  on  the  part  of  the  more  intelligent,  regarding 
some  of  the  simplest  requirements  for  the  care  of  children.  Its 
most  direct  appeal  is  to  the  new  mother,  answering  as  it  does  every 
question  which  lack  of  experience  may  suggest  and  putting  into 
her  mind  many  thoughts  that  would  not  occur  to  her  at  all,  but 
which  Baby  is  sure  to  profit  by.  The  book  does  not  stop  here, 
however,  but  continues  as  a guide  up  to  the  seventh  year.  A new 
edition  is  now  ready,  thoroughly  revised  by  the  author,  and  all  the 
latest  results  of  experiment  and  scientific  treatment  incorporated. 

What  the  Authorities  Say. 

“Just  the  thing  to  put  into  the  hands  of  a young  mother.” 

— Medical  Standard. 

“ The  cost  is  so  moderate  that  it  would  pay  doctors  to  make  a present 
of  the  book  to  deserving  mothers  and  nurses.” 

— Virginia  Medical  Semi-Monthly . 

“It  combines  simplicity,  brevity,  and  exactness  upon  such  points  as  a 
child’s  nurse  needs  to  know.” — Medical  World. 

“It  is  indeed  a condescension  for  Professor  Holt  to  have  written  this 
humble,  simple  little  catechism,  but  that  is  but  a sign  of  the  author’s  true 
greatness.” — The  Hahnemannian  Monthly. 


D.  APPLETON  AND  COMPANY,  NEW  YORK. 


6U^ 

— s- . ' ^ 

Uis  ty 


